u can do this with the motor installed in the vehicle
like kai said u will need to pull the head and take off the pan
then remove the baffle plate and oil bridge. at that point u can leave the crank in and just carefully remove the connecting rod nuts, remove the connecting rod caps one by one and carefully tap the piston out of the top of the bore using a wooden handle from the bottom. its really tight around the crank but in your case i would recomend leaving the main bearings installed to prevent a problem down the road. so dont remove the crank.
also cover the connecting rod bolt studs with plastic tubing pieces so you dont scratch the cylinder bore while tapping them out.

you can take the old rings off with your hands
then u will need a ring spreader to install the new rings...
u will also need to install the rings in a certain way so the gaps dont line up...this is in the helms.
a special tool is used to compress the rings so you can tap the pistons back into the bore.
you will also be changing the head gasket to reinstall the head.
the helms manual and a TQ wrench is going to be a NECESSITY on this one, you will need the proper TQ specs and procedure for reinstalling the oil bridge and main bearing cap bolts. not to mention the connecting rod caps and nuts procedure.

IMO its easier to pull the whole motor and then rebuild it, reinstalling the timing belt with the motor in the car will be a bitch for sure.

i can pull a h series in about 5 hours in my driveway start to finish.
this is a sticky situation and you are gonna have to decide what you want to do and make a solid game plan.

ive attached some high res pics from my numerous H22 engine builds to help you comprehend what i was describing
good luck

~kris