Just took mine off today. There are 2 spring loaded pins that need to be removed first. There the black ones that are pushed through the sink on the gpu side and go through the board. Pinch them on the bottom side with some needle nose pliers, and they pop right off.
From there, gently pry the sink of the gpu with a screw driver, use something for leverage so ya don't dork up the card( I used a pad of post a notes). The epoxy used wasn't all that tuff, not much force was needed. Thats the long answer
Short answer
Pinned and epoxied
Ps.
I think it's a good idea to lose the stock heatsink on the Visiontek card. I went from running the stock sink at 47C to 38C with a Blue Orb.
Don't throw the old one away, though. Changing the heatsink can void your warrantee, so should something happen, you might want to slap it back on before you rma it.