Goldaine

Hi, I have recently installed the attack of the b-team modpack on my laptop running windows 8 64 bits. Noticing that I have crashes and difficulty running the modpack, I installed Java 64 bit, so I had more RAM allocation options in the launcher. Now the problem is that even if I allocated 4G to AoTBT, every 10 seconds I have a lag spike, and I know it's because of the RAM because when I press F3, I see the 99% of the allocated RAM is being used, which is normal, because the RAM allocated is only around 400mb. Now this is very weird, since I have allocated 4G to the game... I cannot find a way to change the amount allocate, it won't let me change it I have also messed with the Java Runtime Parameters, trying "-Xmx4G", to allocate 4G, but nothing works. I am absolutely certain I have installed the 64 bit version of Java... What can I do? Why won't it let me change the allocated memory? I can also mention that I have Optifine installed, the Ultra C6 version. Thank you for your help!