A lot of people will be upgrading to Snow Leopard this weekend. There’s the right way to do it, and there’s the wrong way.

Here’s how to do it right.

When it comes to upgrading to Snow Leopard, you’ve basically got two options: upgrade Leopard or wipe the old OS and start fresh.

Upgrade: This is the easiest option — simply upgrade. Install Snow Leopard right on top of your existing Leopard install. Apple recommends this, and in most cases it’ll be an easy, painless upgrade. Of course ‘painless’ is a relative term in Cupertino, and if our experiences upgrading from Tiger to Leopard are any indication, this option leaves us a bit wary. Not to mention, over time our computers become crud-magnets; collecting up all order of detritus.

Our recommendation:

Start From Scratch: Here’s what you should do: wipe your drive and start from scratch. That sounds radical, we know, but we’re such big fans of this option that we actually do this every six-months, wether or not there is an OS upgrade to be performed. You’ll be amazed how snappy your ‘old’ Mac is when it’s starting on a pristine new disk.

Ingredients:

Singular – a shareware program and automator action for finding duplicate files.

– a shareware program and automator action for finding duplicate files. Omni Disk Sweeper – now freeware from our friends at OmniGroup, this will help us clean slim down our drives

now freeware from our friends at OmniGroup, this will help us clean slim down our drives Carbon Copy Cloner — a freeware/shareware app that makes a bit-for-bit copy of your hard dive. Usually used for making backups.

— a freeware/shareware app that makes a bit-for-bit copy of your hard dive. Usually used for making backups. Extra hard drive or external hard drive (preferably Firewire) – Firewire is faster, and only Firewire drives are bootable , so get a Firewire drive if you want to make sure you can roll back to Leopard if anything goes wrong (or mission-critical software is incompatible with Snow Leopard). Otherwise, you can use a USB2 external drive.

The recipe:

Step 1 – Put your hard drive on a diet

More than saving space, you will ultimately save time during the upgrade process if you’ve removed most of the useless garbage from your drive first.

Start with Singular, drag your most likely suspect folders (Documents, Photos, Movies, Music) to its main window and start killing your duplicates

After you’ve cleaned up all your redundant files, now it’s time to ‘sweep’ your disk. Our hard drives always seem to be shrinking, and it’s often hard to tell where most of that space goes. Fortunately, our friends at Omni Group have a utility just for that.

Give it a whirl, and you may be just as surprised as we were to learn that your ‘Downloads’ directory is taking up half your hard drive.

Step 2. Create a Reliable backup

Update: Reader Ben G, advises us (and we’ve confirmed) that Intel Macs can indeed boot from USB 2 now.

If your Mac supports it, we recommend a Firewire external drive. Not only is the sustained transfer rate of Firewire MUCH faster than USB, but it’s the only kind of external drive that your Mac can boot from.

To create a bootable backup of your main drive there is only one choice, Carbon Copy Cloner, and it’s push one button simple. Just remember to make your backup drive bootable, you will have to completely wipe your destination drive.

Now, depending on the size of your hard drive, you’ve got a chance to watch either the standard, or extended version of Lord of the Rings.

Once CCC is done, reboot your Mac with your external drive still connected, holding down the option key to boot from the backup drive. Make sure everything boots up, poke around a bit, make sure everything seems to be working.

Pop the installer in, power down your Macintosh and unplug your backup drive, it would be a cryin’ shame if you accidentally installed over your backup.

Step 3. Install Snow Leopard

Very straight forward, only remember you’ll need to wipe your hard drive first. This is easily accomplished from the installer, just select the erase and install option (remember to breathe, it’s okay, you booted from your backup right?), and follow the remaining onscreen prompts.

Time to watch that episode of House you tivo’d.

Step 4. Migrate settings

On booting Snow Leopard, your Mac will boot up just like it did when you first took it home from the Apple Store –heck that feeling alone is worth doing this every 6 months.

You’ll be presented with an option to migrate files and settings, select “Other Mac” and plug your external drive back in. Now if you select the default option of copying everything you’ll be back where you started, why not do what we do, don’t migrate anything you haven’t used in the past 6 months.

Time to watch The Two Towers, extended version with director’s commentary.

Now the reason we love this process is you loose a lot of the garbage that builds up in systems over time slowing them down. It also gives you an upgrade process that is completely non-destructive and reversible.

The disadvantage is that things that require “device drivers” like VMWare/Parallels, or Little Snitch, or what have you may need to be reinstalled to work properly (just as with any “Migrate me from my old mac” upgrade).

If you need more detail, the fantastic Take Control series has a pair of new PDF ebooks to guide you through the Snow Leopard installation: “Take Control of Upgrading to Snow Leopard” ($10) and “Take Control of Exploring & Customizing Snow Leopard.” ($15). Both highly recommended.