How to upgrade WoW trial with game installment?

If i make a trial account on WoW and get it to lvl 20 before the trial time runs out, how do i upgrade it if i bought the game? It says the game comes with a free 30 days so i can i upgrade the trial to a normal account for 30 days? also when the 30 days runs out will the account just stay untouched until i get another 30/60 days or will it be deleted after a period of time? Main question: HOW DO I UPGRADE WoW TRIAL WITH THE GAME? btw i have not yet installed the game or done anything with it. When i install it how will i upgrade the trial? please answer