You can sometimes take ownership of the folder with the files in it and then you can gain full access to the files to delete them.
1. Open explorer and browse to the folder in question
2. Open properties of folder and select Security tab
3. Click on Advanced button
4. Select the Owner tab
5. Select a new Owner from the list
6. Tick box for 'Replace owner on subcontainers and objects
7. Click ok twice.
