Fire Emblem (GBA) help

I bought a used copy of Fire Emblem (not Sacred Stones) and the prevous owner beat everything you can possibly beat in the game. I want to know if there is any way to clear all the data from the cart. I erased all of his files and started a new game, but everything is still unlocked.supersruzz

I think there's some sort of button combination. I know that select is involved in there. 

There's a button combo for soft reset, but I don't know if there is one for clearing data.supersruzz

There's one for that. I just don't know what it is. Look in every walkthrough.