How do I remove my graphic card from a Dimension 9150 ?

I've never switched graphic cards before on any pc.

And now it shows that I have a dimension 9150 and I have no idea how to remove the graphic card.

Here's a picture 

http://www.google.se/imgres?imgurl=http://img.tomshardware.com/de/2006/07/04/vergleichstest-intel-viiv-pc-computer/dell-inside1big.jpg&imgrefurl=http://www.tomshardware.de/vergleichstest-intel-viiv-pc-computer,testberichte-1509-5.html&usg=__mEqXJ2HyLc63ziEKexCR_CaXRT8=&h=1332&w=1314&sz=192&hl=sv&start=0&sig2=ct_wNU5BgET6I9horFqYLw&zoom=1&tbnid=3lLO4WYyoLrXOM:&tbnh=159&tbnw=157&ei=Lhj9TIeGIMucOvCh5dUK&prev=/images%3Fq%3Ddimension%2B9150%26um%3D1%26hl%3Dsv%26sa%3DN%26biw%3D1024%26bih%3D677%26tbs%3Disch:1&um=1&itbs=1&iact=hc&vpx=374&vpy=293&dur=14&hovh=226&hovw=223&tx=106&ty=153&oei=yhf9TN-qAcGCOqHO-N4H&esq=17&page=1&ndsp=12&ved=1t:429,r:5,s:0

anyone? :emotion-42: