How do I know my ram capacity?

[Jessica Fletcher]

Hello,I'm looking to upgrade my sdram. I seem to have only 3 sockets(?) Right now I have 2x256 pc133 sdram and I'm wondering if I can swap that out for 2x512 or add 1 512 to the 256 I now have. Thanks

 

[GhislainG]

What motherboard or system do you have?