Its a straight forward Job But Before you buy any Memory stick They go in But they also may not work.

Has to be a Matching set
so Unless you can see what value sticks are in the Slots and How many "free" slots
Plus several other Numbers such as the Processor
Make and Model of the Motherboard
But rather than Sticking your head in the Works Looking for all that (and straining your eyes)
Download and run SIW from
www.gtopala.com only a few seconds choose
SIW Standalone quote:
SIW - System Information for Windows
Everything you want to know about your computer
SIW is an advanced System Information for Windows tool that gathers detailed information about your system properties and settings and displays it in an extremely comprehensible manner.
And it does what it says, generates a really long informative list

And you can take it with you on a memory stick 1.7 MB(Does not install into Windows)
Scroll down to the Hardware section and you find all that Info and More besides
With that information we can give you some prices and show you how to swap over the sticks
when the Time comes Is about a 1 to 2 minute job per stick Tops
Ps Also need to know what Size memory is currently Fitted?