Another very easy achievement in this game.
EDIT: it seems to be the case that you have to be at least lvl.5 to gain access to the hero menu. This wasn’t the case a couple of years ago and was added by an update.
On the world map press Y and open the menu. Go to the section "hero". There you can change the outfit, gender, race etc. of your hero.
Just change the outfit and the achievement will unlock. Pretty much effortless.
Hope this helps!
Any improvements? Please let me know in the comments below!