Well first, you see on the top-right that slot your GPU is plugged into? There is a small lever on the left side of that, push it up to unhinge your graphics card's interface from that slot. Then you will have to look how to unlock that card from that unit. This isn't a normal setup so I'm guessing here, it looks like there's a latch on the left side that may be holding your card in place, if not try looking around to whatever is physically holding the card in place.
The only thing I needed to let you know was that interface connection, if you tried yanking it out without pushing that lever down you could've damaged that slot.