I assume you mean getting more memory when you say “buy more speed for it”. In my view, adding memory is always a good idea to give a sluggish computer a boost.
In this case though we’d recommend you give your computer a clean up just to see if that will give it a speed boost. First, try uninstalling any unnecessary programs. Only remove programs you know and don’t use: If you don’t know what it does, leave it alone.
The next step is to make sure your system is clean with a spyware check.
With all of that done, it can be worthwhile checking your disk for minor errors. The Chkdsk tool built into Windows is as good as any.
If you find all of this hasn’t improved speed then you should speak to your local computer tech about the upgrading options.