From the rear of the board, find the two plastic pins that hold on the sink. Squeeze the prongs of one pin together and pop it thru the board, repeat for second pin.
I found I could perform this task with fingernails (required effort), if you use tools be very careful not to scratch the mobo as you could break a trace and kill the board.
If you find a plasticlike shield on the bottom of the sink, pull it off and use it between the chipset and your new sink.
(Note: And you might want to prune down your signature, I believe you are over the limits. Mine got pruned to its current size by the helpful moderators.)