If you're looking for lead changes, the best way is to counter canter. So what you need to do is pick up a counter canter and lope some circles in the counter canter. The horse won't like it and will want to change leads, but make sure to hold him in it untill you ask for it which I have been taught to do by turning your head, and pressing with the other foot. The horse will do this willingly. If you do it often enough, the horse will soon do lead changes on command, just remember to cue him properly.