first thing you're going to need to do is narrow down exactly which model 20334 you're working on.
partstree dot com - scroll down a bit on the first window - click "Toro" - next window type 20334 into the "Search by Model and Brand" window - that will give you a list of all 20334 models by serial number and year.
then select "rear axle" and you'll get an exploded view diagram of the rear drive axle. enlarge the image. take a good look before you go outside with your tools. take your cellphone camera with you. (if you've got a printer, you can right click on the image and select "save picture as", save it in *.gif format, and print it out for reference.)
remove wheel, step washer, retaining clip, drive pinion gear, thrust washer, the plastic dust cover (they're calling it "wheel cover"), pivot arm, adjustment lever, bracket.
got photos of how that looked before you took it apart?
now the fun begins.
now you have to take off that little sleeve bushing and that retainer.
retainer might be frozen on the axle shaft.
penetrating oil, patience, and tenacity.
if the bearing is already shot, you can go ahead and beat the crap out of it with a hammer, but don't start pounding on that retainer because you'll break it - they shatter. if a guy had the right puller it might go easier.
then you finally get to the bearing.
Toro part number on the bearing is in that list, but I'm going to go out on a limb and say it's probably just another little sealed bearing that you may well be able to find at a parts store or some hardware stores.
you took photos of it, right?
then put the mess back together.
that kind of stuff is why people buy new lawnmowers. actually not really all that difficult, but you're going to get your hands dirty and probably say some bad words before you're done with it.
highly recommended: gloves, penetrating oil ("Knock'er Loose", "PB Blaster", etc.), more penetrating oil.
don't do it out on the lawn - you'll lose pieces and they're spendy at the Toro dealer and they all have to be special-ordered and they won't be here until next week.
(ask me how I know this.)
(* I am NOT seeing any snap rings in those illustrations, but if you DO run into a snap ring, you're going to need some stout snap ring pliers because all that monkey-motion will most likely be corroded and all stuck together once you get past the dust cover.)
be sure you take photos as you disassemble it. don't rely only on those exploded-view diagrams - sometimes they can be no help at all.
** almost forgot: drain the oil and gas first or you're going to have a mess!