When I choose to check for system files it shows about 950MB for previous windows installation but after I click ok and confirm deleting them, it show the deleting process, ends without showing any message and after that when I check, the free space on my drive has not changed a bit even after restarting. I repeated that process and each time it shows the same thing but doesn't remove them. What might be causing this problem? Is there a way to remove those files manually?

When I choose to check for system files it shows about 950MB for windows update cleanup.

After I click ok and confirm deleting them, it show the deleting process, ends without showing any message and after that when I check, the free space on my drive has not changed a bit even after restarting. I repeated that process and each time it shows the same thing but doesn't seem to remove them. What might be causing this problem? Is there a way to remove those files manually?