More RAM can make the computer faster, up to a point.
If you are running a 32 bits version of Windows, you can't benefit from more than 4 Gb of RAM as it's the largest quantity of RAM that your system can adress. In this case, adding more RAM is totaly futile.
If you are running the 64 bits version, then, it's recomended to have at least 8 Gb of RAM. If that's your case, adding another 4 Gb of RAM WILL realy improve your performances. You'll go from minimal RAM to recomended RAM. In this case, going to 12 or even 16 Gb can slightly improve your performances.
Next, do some cleaning:
You should uninstall ANY toolbar. Most are useless anyway.
Also, uninstall any application that you don't use. You may find many that you don't remember ever installing. Those are probably the result of parasitic installs that often come with some legitimate applications installers.
Periodicaly do a cleanup of useless files that tend to accumulate. CCleaner is very good for that task. It can suppress old files from the internet cache, old and forgotten temporary files, and other such stuff. It's probably the safest cleanup utility.
Get Spybot and have it scan your system. it can get rid of many unwanted non-viral but nefarious programms.
Get some good anti-virus, have it set to autoupdate and let it scan your computer.
Some propositions of FREE anti-virus:
AVG from free.avg.com
If you opt to have more than one installed, ONLY one should be set to work in the background. The other(s) should be used for "manual" scans.
For your browser, despite what it's fanbase can say, Chrome IS NOT THE FASTEST browser. In my experience, Firefox is faster, especialy on a lower end machine.
The AddBlock plus addon is a MUST HAVE!
Disconnect is only a paranoid thing.
Install the NoScript addon. Combined with AddBlock Plus, it realy improve your experience and safety.
Defragmenting once a year IS NOT enough. It should be done at least monthly, but ONLY for conventional drives.
You must NEVER EVER defragment an SSD. It can damage them.