Tyrogaming_

Ign Tyrogaming_ help please reply when i go onto pixelmon for example it lags so i press f3 and to the top right it said something like memory usage 86% and going up and wen it reaches 100% my fps drops and it does that Over and over so i watched a video where i can change mb to gb so i tried it when i clicked play the launcher stopped and reloaded back up onto the page so i tried 700 or something like that mb and it done the same thing please reply how to fix