Sylveon Special Attack Boost?

Question

I currently have a female level 82 Sylveon with a 288 special attack it's modest as well. It has held a power lens since level 10 and I basically only level it up against the elite four, can anyone tell me how to get it to its max special attack stat of 350 or if this is even obtainable from my point. Thanks for taking time to read and answer this. Have a good day(:

Answer 1

You'd have to ev train her
iv breed her
and have correct natures

to learn more about evs go here
http://pokemondb.net/ev

Answer 2

350 is maxed out in sp atk ivs, evs level 100, and a nature that boost its special atk. It's not possible to reset your ivs or nature without getting a new one/breeding. You can check your and/or reset your evs in the supertraining for xy though I doubt you would need to if you had the power lens the whole time.