Assuming you pre-ordered a physical copy; you should have a pre-order code on your receipt that you redeem on SE's site for early access. If you do not have such a code, call the Gamestop you pre-ordered from. You will need to pick the game up on or after actual release, at which time you can use whatever method of payment you want for any remaining balance.

I can't help if you pre-ordered a digital copy, as I do not know how they handle those.