If your system is still charged with R12 I wouldn't do it now. The changeover is quite easy especially since the oils are now compatible. Most auto parts stores have the kits. If you want to do a really thurough job you can use a flushing solution and clean out the complete system which means some disassembly to flush the evaporator, condenser and pump. I would strongly recommend changing the receiver drier. Over the years I have done several retrofits on my own cars with good success. Sometimes I did a complete flush and on one occasion I did a quick and dirty just installing the new inlet ports, they all seem to work fine.