Yes you can just delete the windows.old folder
If you backed everything up and have everything you need you can just delete it..and say hello to 46 GB of free space!!
Hope this Helps..
EDIT: Here is a step by step guide Windows.old Folder - Delete Important
Before you remove the Windows.old folder, make sure that there are no important files in it.
- Click Start , click All Programs, click Accessories, and then click System Tools.
- Click Disk Cleanup.
- In the Disk Cleanup Options dialog box, click Files from all users on this computer.
Note If the User Account Control dialog box appears, type the administrator password, and then click OK. Otherwise, click Continue.
- In the Disk Clean up drive Selection dialog box, select the hard disk drive that you want to clean up, and then click OK. Wait while the system scans the computer for unnecessary files.
- Click the Disk Cleanup tab, and then look for the Previous Windows installations check box.
- If you find the Previous Windows installations check box, click to select it, and then click OK.