We need specs of your current computer to be able to help.
In all honesty though, since your computer is almost 10 years old you're better building a new one from scratch.
Anyways, if you want to attempt to upgrade your ancient desktop, here's how you can help us to assist you
1.go to search bar in start menu
2.search for dxdiag.exe and run it.
3.either save the file and post it here or screenshot the results and post it.
We can then evaluate what you have and see whats actually still worth anything. If it's really 9 years old then honestly almost everyone is probably dated.
It would probably be easier and cheaper to build a new one though. If you give us a rough budget I can help make the best gaming computer for your money(in terms of picking parts)