In my database, I have two tables: Forum and Files

Files have two fields. First one is FileID and second one is FileAddress.

FileId field is fine. but in FileAddress field I have a lot of urls. I want to just change certain parts of url. For example, instead of having http://IPADDRESS/FILEPATH

I want to chage that to http://domain.com/FILEPATH for about 400 data in the sql table. How do I do this?????

you need a stored procedure, chk this example:
http://vyaskn.tripod.com/sql_server_...nd_replace.htm

you can also use mysql REPLACE function

like

 
UPDATE Files SET FileAddress = REPLACE(FileAddress,'IPADDRESS','DOMAIN')

Note: make sure to backup db before doing trick.