Pretty much just have at it... I start with a small drill bit than go up in diameter if needed. One tip is use a shop vac while drilling because those metal shavings fly everywhere.

You only need a bit large enough to remove the screw holding the plate onto the lock. 1/4" is probably big enough. Use a fast enough drill speed that you're not going to catch on anything when you break through. A shorter bit is easier to control. Two inches is probably deep enough.

I use a 1/4" concrete bit. works slicker than puppy puick

Not sure of the quality of lock Stern is using nowadays, but an option that doesn't involve drilling is using a large, square-shanked flat blade screwdriver inserted into the lock and wrench to twist, shearing the locking pins. Opened many a lock this way. I only drill the stubborn ones.

SR

Pick it instead--way less effort/mess.