SO, the minecraft launcher was recently updated, and the JVM arguments no longer appears when I try to edit a launch setting. How do I allocate more ram now? Edit: My apologies, I forgot to enable advanced settings
Ok, so pretty much D-Inventor's Answer, but easier. First go to Launch Options in the launcher, and check the advanced settings slider
Then, you want to go to the release you want (Click Latest release), and tick the JVM Arguments box.
After that, choose how much RAM you want from this chart:
2GB: -Xmx2G 4GB: -Xmx4G 6GB: -Xmx6G 8GB: -Xmx8G etc..
After you've chosen your RAM, change the part in JVM Arguments that says -Xmx2G (or whatever it says), and replace it with the code in the chart above, and click save. You're welcome :).