Lifehacker explains that while viruses or malware can certainly make your machine sluggish, a number of popular antivirus programs—McAfee and Norton, for example—actually contribute to the drag. You should have an antivirus program, but one way to make your computer faster is to try a free alternative like Microsoft Security Essentials that won't weigh down your system.
2. Try more RAM.
Larger programs use a bigger chunk of the machine's available memory (like games; or basics like Microsoft Word), but running several smaller applications at the same time can also slow you down. It's not always the answer, but adding more RAM can help your computer run faster—HowStuffWorks.com explains in detail. Note: Adding RAM can be complicated; look up your model before ordering what you need.
3. Check your task manager.
It's simple: On Macs, use "Spotlight" search (the magnifying glass icon in the screen's upper-right corner) to look for and open "Activity Monitor." For computers running Windows, press Ctrl+Alt+Del to bring up the task manager. You'll see a list of programs you're currently running, along with how much memory each is using. Click on any application you aren't using, and "Quit Process" to free up some memory and make your computer faster.
4. Consider a memory cleaner.
"Memory cleaning" apps generally deliver a quick boost of speed with the click of a button, but CNET warns: "This process technically frees up RAM, but only in the sense that squeezing a sponge down on a flat surface frees up water-absorbing capability." Once you restart the programs, "they'll start soaking [RAM] back up again."
5. Think before you update your apps.
Your computer might be suffering from "software bloat": As processors become more advanced, developers want to tap into their power to build up their products. That means the new version of your favorite app could be much more taxing than the previous one, even though you're using the "same" program as before. Not updating with each release might help make your computer faster.
6. Remove unnecessary auto-start programs.
When you reboot, some programs automatically start up, sapping your machine's resources. Fix it: On a Mac, click "System Preferences," then "Users and Groups," and then "Login Items." From there, remove any programs you don't want to open when you restart your computer and that should make it a bit faster. For Windows, visit How-To Geek for a step-by-step guide.
(source: http://www.rd.com/slideshows/how-to-make-your-computer-faster)
