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
Already answered on your other forum post.
There is a tab on the bottom of the PCI-E X16 card that releases the card after the screw that holds in the tab is removed.
If this is not clear then you may need to get a qualified service tech to do this for you.
If a "piano" bracket (for full-length PCI-E cards) is present on your computer, rotate it upward by pressing the tabs on the side of the bracket toward each other.