How to allocate more RAM to 1.11?

Hey guys, sorry if this is a noob question.

I've searched the internet and I can't find any guide that works on 1.11. My PC has 8gb of RAM but minecraft only uses 499mb. I've installed 64bit Java and I use Optifine.

Every time I hit 99% mem usage my game freezes, so it freezes every second or so.

Any help is appreciated!

It is working now, thanks guys!