I brought a new pc that should have 1024mb of RAM but when i started it up and looked at the specs it was 768mb and it says it is about 68% loaded.

How do i get it to be 1024mb of RAM?

Hi and welcome to D-A-L

you've maybe got 256MB for your graphics

so the 256 (graphics) + 768 = 1024

so if i was to decrease the graphics RAM would it increase?

yes but then your graphics may suffer (if you can alter the amount)