HSF = HeatSink Fan.. It's a Combo deal, but refered to as just the acronym.
The entire thing has to come off some way. Either by retaining push pins that you take needlenose pliers to the back of, carefully I may add. Screws. And others use Adhesive compound. If you see NO attachment anchors anywhere, then it's probably glued to the chip. If that's the case, get the card warm by running the system, maybe playing a game then promptly shutdown the system and pull the card. **Carefully** try to Twist the heatsink off while your pulling up a lil.. It should break free..
Now a legal note: the above is only my suggestions, it's your hardware, not mine. I take no responsibilty if it breaks..
The general way however that hsf's are put on is with mounting clips or pushpins.. Tho I've known cards that do it this way to 'save money'...
Another thing you could try, if the screwheads aren't rounded off yet, take a mini blow torch to the screws and then try backing them out. Please note: torches are dangerous, you can burn yourself, you can also torch your card, so be very carefull if you attempt this.
Outside of that, I can't think of anything else to try.. Outside of smashing the card to bits and giving yourself an excuse to buy a new one.. lol