@Varkanoid, the only big space saver in disk cleanup for me, is the "previous installation" of 27GB, kinda worried to remove it.. Would it be safe to do so? I know it may seem an odd question.
If you want to rollback to your old O/S within 30 days you will have screwed yourself, and will have to reinstall it if you remove it. Nothing 'dangerous' about removing it though.