Stand next to the seat with your feet flat on the floor and find the top of your hip bone. Adjust your seat so it matches the height of your hip bone.
To change the height, release the pin by turning the T-handle counterclockwise and then pulling the handle to disengage the pin from the seat post. Adjust seat post height and then release handle/pin to lock in place. Tighten handle until snug and post is secure.