If your seat post looks like this:
7/8" round seat post
Use a 14 mm wrench or adjustable wrench to loosen the nuts
on the clamp.
Remove clamp from the seat post.
If you have trouble
getting the clamp off of your old seat, ( this seldom happens)
you may purchase a new clamp from your local bicycle dealer
for about $6.00. Let us know if you need one.
If you need a
new 7/8" round seat post clamp, order one with your seat
Remove clamp from the old seat.
Install the clamp on the new seat.
clamp installation instructions - here
Install clamp on seat post.