PHP sessions timeout

Hi,
just set up a new HSphere account & uploaded one PHP/Mysql website that uses sessions for authentication.
It kicks me off in a few seconds not allowing me to go from page to page and do updates.
How can I set the lenght of sessions for 20 minutes?
Do I do it in local php.ini file in the root of my web site or tech support must do it for me?

Thanks

You can do it in the local php.ini in your web root.