Minecraft doesn't use enough RAM. Help!(with screenshots)?

So I have 1GB of RAM and when I go to propeties is says I do, but when I start MC it say it uses (Procentage here) of 494MB and it allocates only like 150MB, but everytime before i start MC in task manager it says only 153MBs of 1024MB is used(I asume those are the system procceses). Can you tell what it is or how can I make MC use more RAM cuz it did before I rebooted my PC it always said 1024MB and that it's allocated around 900MB but now everything changed, please help…

Right click >> go to process >> right click >> Set priority >> High.

If you mean you only have 1GB of ram then you can't go higher. Other background processes need ram to keep your pc stable. Also allocated ram is how much it used so far in your case it will go up to 494MB. If I was you id say buy more ram at least 4GB.