Google shows that as running Windows mobile by default, but it looks as though there has been a version of Android ported to that handset. Are you running Android on it at the moment?
I'm not sure where to start if it's still Windows Mobile, this is an Android forum and my knowledge of the Windows Mobile OS is about 0, sorry.
If you're using Android, try Settings -> Wireless & Networks -> Mobile Networks -> Access Point Names (or there abouts), there should be an option to edit APN settings there.