yep you can. side grade is going from one product line to another: ie: vue4pro to vue5 esprit is a sidegrapde, or going from c4 to vue5pro is also a sidegrade upgrade is upgrading your product line: ie: vue4pro to vue5pro is upgrading. but in reality who cares what its called realy, its still e.on products, and yes, youll be able to go from vue5 to vue5 pro with a discount as compared to buying vue5 pro as a brand new user (dont know anything about the pricing)