Talk about ancient history. I have no idea how students change classes these days, but back in the 70s you could drop and add classes through primitive computers manned by college staffers. You gave the staffer your request and they gave you a printout of the request showing whether you got in or not.
First you had to stand in line and wait your turn to drop a class from the schedule you were given. Then you stood in another line to add a class to take the place of the one you dropped. After I got used to the system, I did it all the time. It was exciting because you could for example try to trade a 8AM English class for 1PM English class. But if the class you wanted was full, you were screwed. Sometimes I would just keep going back over and over until a class opened up because there was somebody in those long lines who dropped out of the class I wanted.