The system is upgraded to win 10 online, and there will be a windows.old file on drive C, which will be packaged in the previous system, so that you can restore to the previous system within 30 days. If you are sure to only use win 10, you can delete this file (because it takes up at least 10 g of space). Think again, you can wait a month before deleting it. Delete the windows.old file as follows: 1. Right-click drive C directly-Attribute: 2. Click Disk Cleanup (this process takes a little time): 3. Then select Clean System Files, as shown below: 4. This process takes a little time, because. The old folder is quite large and has many resources, so be patient: 5. Scroll with the mouse and select ".