today i reached lvl 60. can any one tell me detail about main changing option? my main now is earth. i see 4 option unlock at different lvl last one at 78 lvl. does it mean if i challenge lightning now and win i become lightning main and cant become water, fire, wind until high lvl? if yes which would be best for me now? if there is already any guide can someone share link pls. thank you in advance