hi Norms, welcome to fiat126uk.
first thing is to make sure that it is the big ends, symptons range from a mild tap-tap-tap to machine gun RAT-TAT-TAT-TAT if they are really shot.
its a fairly easy job to just change the shells(bearings) but often a false economy if the cranksahft is worn/scored or the cause of the problem lies elsewhere, ie; oil pump/oilway blocked, there is also a small drilling on the crankshaft with a plug that is prone to coming adrift
but very basically you need to,
remove the engine from car
remove the sump
remove the big end caps, do not mix them up as they are machined as a unit with the rod
inspect the crank for scoring, measure with micrometer to check it is within tolerance for wear
dry assemble with new shells with plastigauge, strip and check clearance using plastigauge
reassemble with lube and torque up BE caps
replace sump and put engine back in car and drive about with a smile
on your face.
if you do decide to do this yourself then come back to us for a more comprehensive guide
