To move a datafile to a different location:
1. Shut down the database.
2. Copy the datafile(s) to the desired location(s).
3. Mount the database, but do not open it.
4. Issue the following command for every datafile that has been moved.
ALTER DATABASE RENAME FILE 'old_name' TO 'new_name';
5. Open the database.
6. Back up your control file.
If the file belongs to a non system tablespace you should also be able to do the rename by just taking the tablespace offline, instead of shutting down the entire database.