How do I upgrade from 6.5 to 7.5 Cubase?

I bought 6.5 two years ago and now need to upgrade to 7.5 so that I have the same version as we have at school. There is no telephone help accessible on the Steinberg site until January 4th. I would be very grateful if someone could tell me how I go about buying whatever addition I need to get up to the 7.5 version. (If possible using the simplest language possible… I am new to this!) Thanks! :confused:

Google ‘cubase 6.5 to 7.5 upgrade’ and there are several options for the upgrade.