You can upgrade/downgrade and add new features for your account instantly from within the client area.
Or contact Accounts on 01480 26 00 00
Goto client area at https://www.fast2host.com/clientarea.php
Select "My Products & Services"
Select the package for which you wish to purchase addons and click "More options"
Select "Click to view available addons" and order any extra's or upgrades.