Is there anything I can do about it, or should I just buy a different one or build one?
Your RAM amount on the board is tied to your video performance. If you have the maximum amount of RAM in your computer already you'd have to get a new motherboard. Since it is the heart of the computer you may find you either buy a new computer or build a new one. You could just make it simple on yourself and get a pre-built HP.
Here's the options you have that are going to give you a boost, but mediumly priced. Hopefully it'll give you somewhere to start, sorry I don't have better news :P