Actually, you do not need to do any of this. Follow these instructions.
Browse to c:\windows\windows\web\wallpaper
Right click on wallpaper and click properties. Select the Security tab and then click the Advanced button.
Click the owner tab. Current owner is probably listed as System. Change Owner to field should have your currently logged on user listed. This account must have local admin rights to the system to make the next changes.
Click the Edit button. Now click your currently logged on user account under the Change owner to field. Check the box of Replace owner on subcontainers and objects. Now click Ok and confirm you want to do this. Once you have taken Ownership of the folder and subfolders then continue below.
Go back to the wallpaper properties and select the Security tab. Click the Edit button and add your currently logged on user account to this list. Give yourself Full Control permissions and click Ok. Now click the Advanced button and then the Change permissions button. Check the box Replace all child object permissions with inheritable permissions from this object. Click Ok and confirm this. Now all the folders and files under the Wallpaper folder should be under your control and you should have Full access permissions to them. Now choose what you want to delete.
Yes, this is alot of steps, but it is the correct way of doing this. And there is no need to "hack" anything.
I hope this helps!