If you install Windows 7 or 8 by performing a custom installation and don’t format the partition during the installation process, files that were used in your previous version of Windows are stored in the Windows.old folder.
This size of this folder could be huge, several GBs, it’s a must we remove it and claim more disk space. But if seems rather difficult to remove it for we usually encounter permission problems. We just can’t delete it in normal ways.
To completely remove this folder we need help from a Windows built-in cleanup tool.
Step 1. Right click on System Drive, choose Properties.
Step 2. Click “Disk Cleanup”
Step 3. Click “Cleanup system files”
Step 4. Choose “Cleanup previous Windows Installation”, then “OK”
Step 5. Confirm
Now, wait for the cleanup process to be done.