Crank boss off??
Flywheel off.
I assume by the sounds of what you said its apart already.
Use an old blade nut, tip it upside down on a block of wood, blade nut on and drive it out of the casing with a hammer. it wont be overly tight but you will damage the nylock part of the nut but probably not to a point where it could not be reused, ive just got one nut and i use it over and over, they are pretty cheap to buy. The last bit you will have to do holding the crankcase above the block of wood. Remove the nut and take the crank out.
Then tap the bottom bearing out of the crank case with a pin punch or drift. Hone the bore and Clean the crank case up ready to put back together. If you have honed, hot soapy water and wipe the bore out with a white cloth, when the cloth is clean the bore is clean. Dry it well. Oven is good if the sun is not out. The blocks are a bit of a pain as the rough cast bits grab the rag and try and shred it.
The other bearing will come off the crank with a chisel or pin punch, mount the crank standing up in the vice grabbing it where the bearings do not run. Belt the bearing off using the outer race. Ive had some grumbly bearings and not one has blown to bits and last its balls yet.
Clean up the crank. New bearing on, gently, a bit of pipe is a good drift. Make sure this bearing is open both sides, i wash the grease out. Some dont.
Bottom bearing is a special bearing. Should be marked Victa on the bag/box. The seal side is metal and the other side open. You cant just use a regular bearing with one seal side left in it.
Offer the crank up to the crankcase, get the flywheel on, crank boss, and use a rattle gun to pull it all back together. You will need a washer to simulate the blade plate. To get it all together you may need to gently tap the crank down into the housing a little. But take care as this will push the lower bearing out what little you have it pushed in.
Then when you go to put the piston and rod back in be sure and slop a good teaspoon or more of 2T oil down into the bearings under the crank counter weight.
If you dont have the tools you might have a go about a slighlty different way. Just take care of that crank thread.
You talked of pressing so i assume you have one.
If so you could put the lower bearing into the housing and then push the crank in using a plate etc to stop the lower bearing coming out.
Cheers, Bob.
