Can any one tell me how to replace the coolent in my mark 2 1.2 8v punto?

Personally Id let the car stand for an hour or so after last movement on a flat surface,. Take of the radiator cap and leave off, then the bottom pipe which connects into the radiator, this might be a bit rusted, if so get a flat blade screw driver and prise jubalie clip off gently...all the water and crap should drain out> once it has stopped draining replace pipe and pref a new jubalie clip and then top it back up again

Thanks very much. Is it just a matter of pouring new coolent into filler neck? whats the best way to avoid air locks?

first go buy 2 new screw type (jubile) hose clips 30-40 mm, then there are two bleed screws you must undo one on top of rad. 1 on the pipe at back of engine going into heater. un do them. mash the bottom hose clip off, fiat fit an non reusable one, take off top hose put a hose pipe in where top nose was and rince the rad, also put the hose in the expanshion tank and rince some more.
stick hose pipe up the hoses and rince them also,
refit top an bottom hoses with new clips, mix up a gallon of 50/50 soft water and anti-freeze/coolent, slowly fill system right to the top of tank, now squeeze all the hoses for ages, coolent will go down, top up the coolent to max squeeze all the hoses again, repeat this filling to max an squeezing untill water comes out of rad bleed screw, then do it up, then keep filling and squeezeing untill coolent comes out of other bleed screw, do that up, top up to max mark, put cap on, run engine untill hot (fan should come on) then turn off let engine cool untill completly cold check coolent level and top up to max if it needs it.