the easiest way to defeat a simple lock is with a similar key and some jamming. you know how a bump key works? or get a lock pick kit or, grind or drill out the four rivets amd replace with carridge bolts. after that buy a new set of locks. or get a locksmith out to make new keys for it. either way, it will cost money, long term, buying new locks is a good way to go imo, but more difficult to find so it takes more time. locksmith is pretty cheap and fast as ****.
edit... saw the above comment, if theybare numbered, then this is the way to go. cheapest and fastest.