Step 1: Install Java x64 here: https://www.java.com/en/download/manual.jsp (Choose "Windows Offline (64 bit)")
Step 2: Open Technic, and in the top right, click "Launcher Options". Next, at the top, under "options", click Java Settings. Then, under "Memory", set the RAM allocation to whatever you would like.
Note: if you did not install 64-bit Java, you will only be able to use up to 1GB of ram.
We recommend at least 2-4 GB of RAM to smoothly run the pack.