Can I replace this Airwell thermostat?
You really need the manual for your air conditioner system.  There isn't one set standard and things vary quite a bit.  Further I have no idea how standard things are outside the US.

The base plate you show appears to be designed for a Heat Pump.  Do you have one?  (Provides heat in the winter, and cooling in the summer)  If so the aftermarket thermostat will also need to be designed for Heat pump use.  The one you have may not be adequate to handle the emergency heat and changeover valve signals used in a heat pump.

This is the best reference I've found over the years for thermostat wiring: http://wiki.xtronics.com/index.php/Thermostat_signals_and_wiring

My wild guess (not responsible if you damage the unit) is that the terminals labeled Gd (ground?) and R (red) are the hot and common of the 24VAC transformer.  If you have an AC voltmeter I recommend measuring them.

The rest of the signals are just abbreviations for colors.  You will need to look at the link to figure out what they do.  Gn (Green) should turn on the fan.  The Bk/Br lines are a mystery, one of them is probably heating call. P (Pink) might be the emergency/aux heat (usually electric heat strips), Y (Yellow) is probably cooling, and O (Orange) sets the changeover valve to Cool.  

Again, there is almost no way to be certain without the installation manual for the AC unit.