It is the front of the seat that will pull up. Try initially pushing DOWN on the nose of the seat, then turn the key and see if it doesn't release
Yeah... there's a short little cable that the key is supposed to pull that
then is supposed to undo the latch holding the front of the seat. Disuse
can gum up (or worse, crust up) the works. If you can't get it to do right
with Chrisj's trick, maybe you can remove the left side cover and
see what is going on back there... maybe squirt lube, maybe jiggle
the cable. If you still have the owner's manual, it outlines how to take
the side cover off, whatever, don't break its little tabs...
-Mike