By far the lowest cost upgrade a user can make to their computer is the addition of Random Access Memory. If RAM has never been upgraded, the computer is almost assured of being in need of additional RAM. RAM is used by all software that needs to run, and as a result is a physical limitation of the computer that cannot be overcome with any tuning or cleanup.
In addition, RAM is relatively inexpensive and is easy to install. Even if you hired a technician to install the RAM, it can be installed in less than an hour, probably even less time.
Additional RAM can be purchased for less than $50 for most computers. The memory manufacturers make it easy to find your model and determine the maximum amount of RAM that can be installed. A lookup on sites like Kingston, Crucial, or others will help you find the correct memory for your computer model. If you don't know your computer model, you can check the mother board number, if you don't feel comfortable with that, a technician can easily determine the correct RAM.