What is your computer model? Its odd that it says 5gb. Id say thats false. Ram is limited by the OS i think not the hardware. So it would really depend on which version of windows you have. Windows vista 32bit takes a max of 4gb, and if you have the 64gb version then you should be good up to 8gb. Look at this: http://msdn.microsoft.com/en-us/library/windows/desktop/aa366778(v=vs.85).aspx
Schroll down and find your windows version and you will see what your Pc can take.