1 Open Your Minecraft launcher select Your profile and click: Edit Profile

2 At the bottom put checks in Both boxes: Executable :And: JVM Arguments

3 Leave the Executable: alone

4 In the JVM arguments Put the amount of RAM You want to run minecraft with: -Xmx1024 -Xms1024

Xmx is the maximum Minecraft will use. Xms Is the minimum.

5 Here's the key for Gigabytes of RAM

1G 1024
2G 2048
3G 3072
etc etc...

6 Then click save profile and run minecraft.

Remember if You are running a 32 bit system You can only allocate 1G To any given task.
If it did not work You must have had to much or too little Allocated to Minecraft.

Hope this helped please diamond Its appreciated Thanks. -Tykin