And to change your avatar go in options and select avatar options.
He doesn't mean that
It's actually a mod someone made where you can make yourself into a dog (Pet mod is it?)
To change you're player outside of minigames, play a brick, use the wrench on it, hit the Events button and put in onActivate, then Player, then changeDataBlock, then choose whatever one you want, like Horse for example, then hit OK, then click the brick, now you're a horse
Or you could do onPlayerTouch then Player then changeDataBlock and choose Horse, so this way you can walk into/step on the brick and become a horse