Check the back of the card at the bottom for a retaining clip on the motherboard that a simple push with your finger will release.

... depends on the cables, and they'll often be a little sticky if they've been there for a while, but brute force is almost never the correct solution.

Yeah, that's the "sticky" thing. Gently but firmly wiggling them back and forth will almost always tell you if there's a clip or screw or if they're just stuck.

The trick is that you always want to make *sure* there's no clip or screw before you pull any harder.