Like this Gateway SE?http://support.gateway.com/s/PC/2800071/280007101.shtml
On the back of the computer remove the screw from the top middle.
Now remove the screw on each outside edge, down towards the bottom.
Hold the outside shell, or computer cover. Push the inside forward.
The computer cover comes off like a shell, or bonnet.http://support.gateway.com/s/PC/2800050/280005003.shtml
If this is a reference to a Gateway 500X series, remove the thumb screw/s from the back of the computer, on the right side. (Right side as you are facing the back of the computer) Then slide this Side Panel towards the back of the computer.