|Your link doesn't work.|
The heatsink is apparently stuck to the GPU with either thermal paste or thermal adhesive. If paste was used, you *should* be able to carefully work it free by twisting it back & forth. If adhesive was used, you risk damaging the card by removing the heatsink.
According to your other post, you just bought the card. Obviously if it's dust clogged, it was a used card. I'm curious why you didn't clean it before you installed it? You didn't think a load of crap stuck in the heatsink/fan would be a problem?