well 1st you need to disconnect the battery
leave it for a while,lets say an hour
then remove the centre of the wheel
airbag unit removed by whatever means.probably a couple of bolts
once removed it will be a large bolt for the steering wheel
pull the wheel off,may take a bit of pulling.you can leave the nut on the end of the shaft so you dont whack your self when the wheel lets go.
fit a wheel boss
then wheel
this is a ROUGH guide and i dont have a punto plus messing around with airbags is risky. remeber to put the airbag somewhere safe