Our sliding shower door needs one of the wheel replaced, i have ordered a replacement one, but I have not clue on how to refit the door onto the track. I will try to be as clear as i can. The door has 2 bottom wheels and 2 top wheels. The wheels at the top rest on a groove that has a lip, the same at the bottom but obviously the lip is pointing down. Does anyone know how to replace the door once I replace the broken wheel? I have tried to insert the bottom wheel first, and then kind of lift the door up to make the top wheels go behind the lip, but there is not enough play.