How do you evolve larvitar on Pokemon platinum?

level it up to 30
If u have a larvitar and u wanna evolve it to pupitar get it to lv 30 and if u want the pupitar to evolve to tyranitar like i did get it to lv 55 there that how u evolve them simple as that.
use it in battles and and take it out for walks and it should evolve. lol