The Windows 10 Mobile Upgrade Advisor app helps you find out if your Windows Phone 8.1 phone is eligible to install the upgrade to Windows 10 Mobile. It can also help free up space on your phone so you're ready to install the upgrade. When you open the app, it checks your phone and lets you know if it's eligible to install the upgrade, if an update is required before you can install the upgrade, or if your phone can't be upgraded. If your phone is eligible to install the upgrade, you may need to free up some space to get it. The app will recommend files, such as videos or photos, which you can temporarily move to OneDrive or an SD card, if you have one installed. Accept the recommendations, or change which files you want to move. You can even delete some files, if you want. If you move files to OneDrive, you need to use this app to restore files back to your phone after Windows 10 Mobile is installed.