In order to remove the motherboard later on, the CPU cache card has to be removed. It is the card in the middle, between the CPU and the RAM card.

It is held in place via two press-fit connectors, one at the top and the other at the bottom. Use a spudger or other pry tool to carefully lever it out of the connectors. Be careful not to knock any components off of the motherboard while doing this.

While you're here, also disconnect the CPU fan's 2-pin power cable.