go into the 'profiles' section and select 'advanced.' go into your active profile, or create a new one if you like. anything you have that sends you a notification will be listed. simply click on the one you want and change it in there.
after clicking on advanced, then choose the profile you would like to change (for example, normal) then hit the edit button (the button on the left of the wheel) then choose edit, then wheel down to the sound you want to change... in your case, mms or sms textclick on ring tone... and all the choices will come up... save. your done.