Did you upgrade your PC to Windows 10 or you did not do a clean installation?
If so, ever wonder what happened to the previous version of the OS, It probably disappeared into the mists of Windows past, right?
Wrong. Your old OS didn’t get erased; rather, it’s lingering in a system folder called, aptly enough, Windows.old. And depending on the size of that version, it could be hogging a lot of precious space.
Step 1: Click in Windows’ search field, type Cleanup, then click Disk Cleanup.
Step 2: Click the “Clean up system files” button.
Step 3: Wait a bit while Windows scans for files, then select clean up system files. as you can see in the image below
Step 4: Now select drive c and press OK
Step 5: Wait a bit while Windows scans for files, then scroll down the list until you see “Previous Windows installation(s)“.
Step 6: Check the box next to the entry, then make sure there are no other boxes checked (unless you do indeed want to delete those items). Click OK to start the cleanup.