You didn't give enough info to know if you can upgrade your memory or not. If you know your computer/motherboard model number then a 1 minute or less Google search should give you the answer anyway.
My system configuration is follows,
Gateway E series
Windows XP Professional; 2.4GHz Intel P4; 2GB DDR SDRAM 266MHz; integrated Intel 845G/GL 64MB (shared memory); Seagate 500GB hard drive, Samsung DVD r/w
Go on http://www.cpuid.com/softwares/cpu-z.html
And download CPU-Z (free and only 3.6mo), after installation, run it and click on "Motherboard", tell us what's the manufacturer and model, and we'll be able to help you !