To do the rings you need to take the pistons out. To be honest once you get to the point of removing the pistons you really have to consider whether it would be easier to get a new engine.
Anyway, the process is roughly
Head off
Sump off
Unbolt big end bolts
Pull pistons through top (EDIT: they won't fit past crank)
New rings on, insert through top with piston ring compressor; which looks like a collar for the piston that compresses the rings while you tap it back into the bore
There is obviously loads of cleaning, inspection/measuring that goes along with this.
I know when I was looking to replace the rings on mine, they were £80+ for a full set from Fiat, and you are assuming the bores aren't totally ****ed. Probably easier to fit a new engine unless you find a cheap set of rings to gamble with.