Changing the refrigerant will not get rid of the smell. Your refrigerant is on the wrong side of your aircon system to the cabin where your problem is.
Given your car is worth a lot more than mine - I might consider leaving this to the professionals.
However, if you are on a tight budget like me - your enemy is fungus and bacteria in your aircon and heating vents. Your weapons are anti bacteria agents that can be airborne (i.e. an atomised spray). I did this on my previous car to good effect - and it is all out anti bacterial warfare.
I used a car bomb like tcyjohnny linked to. I paid £20 for mine from Halfords though - sadly... Follow the instructions to the letter.
Next, I sprayed a disinfecting spray directly in to the vents. This is the one I used and I used about 1/3 of the can in all.
http://www.dettol.co.uk/disinfecting-spray I also sprayed it on any signs of mould in the car (as mine was caused by a previous owner letting it get damp inside).
Be prepared to repeat this process until all the bacteria/fungus in the system is dead. Then you will have killed the source of the smell.
It worked for me and I wish you luck with yours.
Edit - I also changed the pollen filter. It was in the cabin on that car and well gunked up.
