You mean DOWNgrade?
Do NOT use the death kits that you get at Wal-Mart. The only way to do this properly such that it will last long term is to disassemble, flush everything thoroughly, dump oil from compressor, flush with ester oil, replace filter drier, when reassembling use 134 compatible o-rings with nylog lube, add correct volume of ester oil, seal up, evacuate and charge.
If you are in a very warm climate and you want this system to actually have a chance to keep you cool, you should change the condensor to the largest parallel flow that you can fit in place.
In all practicality, you would be much better served to find and repair your leak and recharge with R12. Changing a system properly takes a lot of time and money and using the death kit is a short term solution that will ruin components in your system causing you to spend much more money later.