How exactly long has it been since it started burning if it hasnt been to far ago then you can just flush a couple times and that should save it but if the plants has lost over 50% of its leafs then it could be to far gone to save and is it the lower leafs that are shrinking
or is it all over the place and last but not least be like a doctor when you are treating your plants dont stop trying to save it because that is when you can really learn some tricks first hand (unless it doesnt have insurance then just let it die LOL)