Many cars use R134-A gas (1,1,1,2-tetrafluoroethane) which is relatively non toxic but
should be avoided where possible. However it is bad for the environment (if you care).
...the fact you are replacing the radiator means in all likelihood the gas has already escaped.
To be on the safe side, perform this in a well ventilated area and have some tissue ready.
Remove the front panels and front frame.
Locate the AC pressure sensor, place a spanner over it and give it a turn anticlockwise.
If you hear hissing, move away until you hear it stop. It's the pressure equalising.
You may also get refrigerant oil dripping from the pipe so clean it up as it drips.
Tighten the pressure sensor back in place.