Computer running just a tadbit slow because you've run out of memory...well let me provide you with a simple option add more memory or what us techie call "RAM"

What is RAM?  Random Access Memory

It's a form of computer data storage in which it allows your data to be accessed at random.

Below is a youtube tutorial of How to Install/Remove Computer RAM

*But keep in mind if you are using Windows 7 32-bit you can add 6 GB of memory but Windows is only going to recognize 4GB.