U need to disable the webclient service. Then only u will be able to delete those files. Here's how:
* Click the Start button and choose Run
* Type services.msc and press Enter
* Find the WebClient entry and double-click on it
* Change the Startup Type to Disabled
* Click OK and close the Services Control Panel
* Restart your computer
Now, run Disk Cleanup again, and those files will be safely deleted.
Hope it helps