Gtx 650 ti boost 1G Problem. (League of Legend) HELP!

I just built a new computer and i had a problem with the amd hd 7700 , it just keeps on flickering and flashing while i’m playing League of legend. Thats the only game i’m currently playing. So recently i switched to a gtx g650 ti boost and for some reason i couldn’t max out league like how it suppose to . I know for a fact that its suppose to easily handle league on max but for some reason it drops below 30 fps when everything is on very high . I have a amd fx quad core 4.0 OC , 8g of ram, Asus mortherboard. I’ve seen people run that game on max setting with the same gpu and gets like 120fps. Is there a way i can increase my fps? I feel like i have the wrong settings but i’m not completely sure. I’m not familiar with computers so any help will be greatly appreciated. Thank You