well it depends. try tightening the crank bolts. they hold the cranks to the bb
if that doesnt stop it it means probably one of 2 things. or if it fixes it but it goes back to wobbling soon
1. the taper in the crank arm(s) has rounded out and you need new one(s)
2. if you tighten the bb wich you need a tool for so you probably cant do it. and the bb is sealed bearings...then the your bb has gone bad
Only one or two special tools are required for the bottom bracket and it depends on the type of bracket you have:
Most unsealed bottom brackets require a lockring spanner (you can tell because the lockring, located on the non-dive side,has notches in it) If the center portion of the non-drive side has flats use an adjustable wrench, unless you have wrench that fits. If it has two small round holes in it you will need an adjustable
Just tighten up the bottom bracket (center portion) until it no longer wiggles, but still spins smoothly then firmly tighten the lockring while holding the wrench for the center portion perfectly still - you may have to repeat this a few times. A tenth of a revolution in the bottom bracket can mean the difference between loose or tight.
That should be enough to get the adjustment right.
But since you have to go this far, you might as well get a crank removal tool and take the time to overhaul/re-grease the bottom bracket. A link that convinced me it was easy (after not having done it in 18 years is: http://www.messmagazine.net/mess/ind...d=95&Itemid=60
Sealed bottom brackets: I don't have one, so someone else will have to chip in.