delete / rename a file

Hello everyone.
How can I delete, rename, replace a file (C # isolated storage windows phone 8) ...
I tried it with the following lines of code but does not work:

            File.Delete ("fff");

            File.Copy ("tempfile", "fff"); / / Rename

            File.Delete ("tempfile"); / / Delete

I simply need to rename tempfile in fff and then delete tempfile.

Thanks in advance for your help