Cannot get new belt on

It is not the motor shaft, but the driver shaft or the other little wheel that the belt is supposed to go around. The roller brush part we get, but when we try to remove the other wheel or diver shaft, it will not come out and there is no way to access it. When we changed the belt the old one had already busted, therefore we did not see how it was originally. I have changed a lot of vacumn belts and no it should be simple,I am not sure what we are doing wrong. the vacumn is only about 9 months old.