When the license expires for a MAX+plus II BASELINE, you have to visit the official website and log in with the customer numbers assigned to you and then renew it from that location. There isn't anything that you have to do on your PC since the license is attached to the network and once you made the payment, it should activate itself or you simply click activate and that's it.
To log in to your member's area, access the following link. For license acquired in physical form, contact the developers and ask for instructions.