How to decrease RAM in Minecraft?

I haven't been able to run Minecraft on my new pc and I'm pretty sure that this is the problem, too much ram

If you haven't set it to anything previously, then it'll be the default, 1GB. Don't lower it more than that, bad things can happen if you do.

Too much ram is not the problem. What exactly happens when you run it? Does it not run? Is it slow and laggy?

How much memory do you have? What video card do you have?