The two hull parts should now be separated from each other. Remember how the USB-cable is located so that you can put it together as it was later on.

Remove wheel

Piece of cake, just remove it. No cables or wires attached!

Same procedure here, the board is not fixed to the lower hull. Bear in mind that static electricity can harm electronic components. If available, put the board on an antistatic bag (one of those bags your mainboard or grafic card was wrapped in)

Remove buttons

This task is a little tricky.  You have to release one button at a time. Press down the small nose as shown on the image and lift the button with your other hand. It should pop out of its place.

Do the same for the other button.

When  both buttons are released, you can remove them by sticking your finger between them and the upper hull. Then you can easily remove the two buttons from the hull.