The next image skips a step; Once you remove the top of the disc drive, the disc tray below it will need to be moved to progress to step 6. To do this, plug the console back in and push the eject button. Be sure to unplug the console again before moving on.
There are two versions of the Super Nintendo- the one pictured here, and one with a sound chip board behind the game cartridge reader. These two models have different shells that are not interchangeable (important to know if you're looking to buy a replacement housing for your SNES)