Reclaim Disk Space After the Windows 10 Update by Deleting Old Builds�. Okay, if you just upgraded to Windows 10, don't try this at home. While you can reclaim a lot of disk space by deleting an old Windows installation, it isn't wise to do it until you are absolutely certain that you won't want to go back. I am just now deleting mine from my previous Windows 7. But, if you are sure you won't want to roll back history and return to a previous version, this is how to do it. Unlike my reversion to my Note 3 while my Note 4 now is used as a video and audio server, and for Virtual Reality, it isn't as simple as picking up another phone. But, the benefits can be significant if you do it. My SSD for my tablet is only 128 GB. While I have a Micro SD that adds another 128 GB, my boot drive was running out of space. By deleting the old Windows installation, I gained back 8 GB of storage. Outstanding.