Just like everything else in computers the memory is always getting bigger. Just a few years ago machines would come with 1G of ram or less. Now you won't find a computer with less than 2 Gigs and probably more.
In the past, one of the most common upgrades for computers was RAM. Increasing the memory from 1 gig to 2 gigs would make a huge difference. We still get a lot of people wanting to upgrade their memory.
Now upgrading your memory may not help you. If you are a typical user that runs the internet, email, Word and Excel spreadsheets it really doesn't take that much memory. Once you have enough memory to run your programs more won't really help.
For example: A high usage program like Adobe Premier does run 28% faster with 8 gigs of ram instead of 4 but if you upgrade to 16 gigs you only get an additional 3% increase.
If you are a big online gamer then it is time to consider more RAM, other than that contact me and we can discuss if more RAM will help or if something else would be a better investment to make that machine faster.