I have an issue where I cannot change my Ram, or well I can, but In-Game I will still have 455 MB. It occurred yesterday for the first time when I was checking a singelplayer map. I had a framerate drop so I checked F3 to see what my FPS was. It was only like 30-40 FPS, then I checked the Memory used, and then I saw that the Memory cappacity was only 455 MB, while I configured it to 3GB. I quit minecraft and restarted the launcher to see if something had changed in my profile settings, which wasn't the case. I have tried some things like switch profiles, with Optifine, without Optifine, with Forge, without Forge. However it all didn't work. Check the pictures for the settings and actual Memory.