first go into database and set up two actors, one with the main spirit and the normal stats, and one with the dragon spirit/ better stats, set the second one with the dragon battler, and the first one with a normal battler. (i named mine adam normal, and one adam dragon) also make sure in the last tab of the databse, in the starting characters, whatever you named his dragon version is not in the lineup...and his normal version is the first player.
lost yet? if no continue.
try and set this up as a normal event on the map with no pic and a trigger or parelel process
in the second conditional branch, select script and paste his : Input.trigger?(Input::A)
now by defult, when seomone presses A in game you should be able to see your spirit change, and in battle character change if you set it up right.