Transformer changing forms?

It's been many, many years since I have seen a G1 cartoon--how did the Transformers get their forms? Can they change forms whenever they want?
Now, in Beast Wars in an episiode (I believe it's called Agenda) Megatron visits the Ark--am I mistaken or did Optimus and Crew have a vehicle form?
Are the Maximals and Predicons programmed with beast forms at their release from protoform?
Deep questions that I need answered...that and when the hell is Rhino going to re-release G1 on DVD!?
Now, in Beast Wars in an episiode (I believe it's called Agenda) Megatron visits the Ark--am I mistaken or did Optimus and Crew have a vehicle form?
Are the Maximals and Predicons programmed with beast forms at their release from protoform?
Deep questions that I need answered...that and when the hell is Rhino going to re-release G1 on DVD!?