Stirrups are best adjusted when you are in the saddle. Stand up in your stirrups and you should be able to slide your hand flat under your crotch. This is approximately 3/4 inch. Consequently when you go from a walk into a trot or run you will stand up in your stirrups. Do not use what you see in the movies as a way to ride. Unless it is an old western when the boys could really ride. As they said about the horse cavalry when they charge they "rise up in their stirrups." There are quick-change buckles but if you are the only one riding your saddle there is no reason for these; just use the laces on the leathers. Best if you have someone helping while you stay in the saddle or you can get on and off to make the adjustment. That is what they meant by adjusting on the ground.