Instructions
Place the saddle on a sturdy stand, in a spot where you can easily reach both sides of the saddle.
Reach under the stirrup leather and find the buckle mechanism. Some western saddles use a sliding buckle to raise and lower the stirrups, while others use a buckle with prongs that go through holes in the stirrup leather.
Remove the buckle from the holes and grasp the stirrup. Pull the stirrup down until it comes free of the stirrup leather. Note the hole the stirrup was in, since you need to put the new stirrup in the same hole.
Slide the new stirrup onto the stirrup leather and secure it in the same hole the old one was in. Move the buckle down into place to secure the stirrup.
How to Replace Stirrups on a Western Saddle
If you like your western saddle but not the stirrups, you can buy new stirrups and put them on rather easily. While changing stirrups on a western saddle is a bit more complicated than putting new stirrups on an English saddle, it is not that difficult or complicated. If you can raise and lower the stirrups and adjust the stirrup length, you can change the stirrups on your saddle in a few minutes.