Unlocking file

Hi out there, I want to rewrite a file which is locked by the system
(but not in use).
How can I unlock it for rewriting?

TIA
- Ulli -
===
"On no account allow a Vogon to read poetry at you!"

Ulli Conrad
ucon...@gmx.net
http://www.gwdg.de/~uconrad1
Public PGP-Key at http://www.gwdg.de/~uconrad1/upgpkey.asc