Hi Dave, I replaced that seat on my Voit Mariner which is essentially the same horseshoe/seat as you have. The kind folks here walked me through the process.
Just use a brass pick to carefully pop out the old seat. You will see the holder is curved inward around the top to hold the seat in place. That is the only thing holding the seat in place. I was advised to put a drop of superglue in when I popped in the new seat and it worked great. Not sure its necessary. My 2psi. Good Luck!
"The diver who collects specimens of underwater life has fun and becomes a keen underwater observer. .. seek slow-moving or attached organisms such as corals, starfish, or shelled creatures." (Golden Guide to Scuba Diving, 1968)