This link contains some of the upgrade options available for you : http://www.crucial.com/usa/en/compatible...
This video will show you how to perform the upgrade. Be careful when your system is open and exposed.
(I am not responsible for any of the external links contained in this post. I have reviewed the links provided to the best of my knowledge and determined they are appropriate to this post.)
Update: In reply to your comment:
I suggest that you bring it to some locale place if you are that perplexed by this. Most newer laptops have something on the bottom that will open similar to the cited video. Look at the bottom of your laptop and see if there is any cutout area with small screws. If there is open it, if you see a hard drive then you can just slide it out and follow a similar procedure to the video, however, I would not suggest tearing apart your system as they are so easy to break these days.
Short answer, If you can't figure it out; bring it somewhere. But please, DO NOT BRING IT TO BEST BUY. I'm telling you. Don't do it.