Slowly but surely, Microsoft is getting users to leave Windows 8 behind and move on to Windows 8.1.

According to Netmarketshare, usage of Windows 8.1 reached 6.35 percent of the overall operating system market share in May, finally moving ahead of Windows 8, which snagged 6.29 percent. While Windows 8 usage declined by 0.07 percent last month, usage of Windows 8.1 grew by 0.47 percent.

Another metrics firm, Statcounter, still shows Windows 8 in the lead, but its share also appears stagnant, while Windows 8.1 is on an upward trajectory. Windows 8.1 will probably pull ahead in Statcounter's figures over the next month or two.

Netmarketshare Netmarketshare's May 2014 operating system statistics.

More than anything, the shift toward Windows 8.1 likely has to do with new PCs being pre-loaded with the latest software. But the fact that Windows 8.1 is a free upgrade, with some major improvements over Windows 8, may have encouraged some users to grab the new version. (The free upgrade to Windows 8.1 has also compelled AMD to stop stop supporting Windows 8.0 with its graphics drivers.)

The rise of Windows 8.1 wasn't the only bit of good news for Microsoft. Both Netmarketshare and Statcounter show Windows XP usage falling by roughly 1 percent over the last month. Microsoft stopped supporting Windows XP in April, and has been pushing users to leave the 12-year-old operating system behind.

On the other hand, usage of Windows 7 increased in May, and now accounts for more than 50 percent of all desktop operating system usage according to both Netmarketshare and Statcounter. It is by far the most popular version of Windows available, and when extended support ends in 2020, Microsoft may have to make another Herculean effort to get people to move on.