Help With Memory Allocation!!!

[Rampage65]

Hello. I am running tekkit classic with 4gb of ram dedicated to it alone, however it is still very laggy. I pressed F3 to see what my FPS was but i saw something else. It said that i had like 430 mb of ram or something like that but that's not important. Next to it, it said Used memory and that had a number and a percent. The percent and number kept increasing but as soon as the percent got to 35% it went back down to 17% and kept doing that cycle. Please help i would really like to play tekkit soon. Thx to anyone that read this.

By the Way my laptop is an Alienware M14X R2 with a 64 bit java with 6gb of ram

[Viiwee]

Did you change how much ram is allocated to it in the options menu of tekkit?

Also, tekkit takes alot of ram, and changes really fast.