Use the plastic opening tool to lift up the top panel all the way along the keyboard until it loosens.
It may be helpful to first pry at the rear of the hinge covers (not shown) to release them. Then Insert the plastic opening tool underneath the top panel's sides and then front edge.
Lift up on the front edge of the motherboard while gently prying the case away from the ports on the right side of the computer.
Repeat with the left side.
There is a button for the card slot on the left side of the computer that may pop out if pressed. This button must be held in place while removing the motherboard.
I found this guide to be very helpful, well written and easy to follow.
Close up pics of any connectors, wires and cables that are disconnected help me a lot in that many of my projects have been previously attempted by others who have damaged or wrongly re-assembled the items.