Hi,
I ask this question before until I found my own answer. I delete mine via the cleaning of OS, the procedure is:
1. after logging in as administrator, open up the explorer.
2. select the C: and then right click the c: and open up the c: properties
3. Under General label select Disk Clean UP
4. select system clean-up
5. You find the windows.old and other obsolete system files there you can delete them safely.