Changing coupler for beginner

[Cuffer]

Very new to this and want to simply change the coupler. My son and I are afraid to remove the wheels for fear of breaking something. I don't see screws or anything to remove the wheels and popping them out seems a terrible risk. EMD GP40 Diesel. A video of this would be awesome. 

[Cuffer]

We figured out how to remove the outer cover to get access to the top of the coupling. Broke a few nonessential things along the way. It works and we can now could away!