Hey Greg,
Overheads are notoriously difficult to cast, but here are some tips.
The easiest way to cast overheads is buy setting the cast control knob correctly (see further down) and using your thumb to furhter control the speed of the spool.
Also, don't try & cast too fast - the whipping action of casting can be devistating on the spool if you try too hard.
The cast control knob, generally on either side of the reel, is a small knob that you can use to tighten the mecahnism that holds the spool inn place. To get it just about right, try this tip.
Wind your bait or lure to your rod tip. Put the reel in freel-spool, take your thumb off the spool and let the bait drop. A well set cast control should let the bait drop, but stop the spool as soon as it hits the floor. You may need to trial your reel to get this right, but it will really help.
Good luck!