My 2010 Macbook Pro came with 4GB of RAM and was getting slower over the years when I ran multiple apps. I wanted to upgrade it to 8GB (2 x 4GB memory sticks).
The installation of new memory took approximately 10 minutes. I followed the iFixit installation guide - very easy with the photos detailing where to focus your attention. Having the proper tools improves your chances of success enormously, which is why I ordered them here.
Mac OSX Yosemite runs wonderfully on it with this upgrade.
BE sure to look at the repair guide for your exact year and model - there can be confusing differences between one year's model and another - the exact right one will be very easy to follow with your hardware.
You will have to remove 10 screws to detach the case back - the screws are not all the same, and several are not interchangeable. What I did is draw an outline of my Macbook on an 8.5x11 piece of paper, marked the side that is the laptop hinge, and as I removed each screw, I simply taped it to the paper in the approximate position I removed it from. I had no problem returning them to their exact original position.
Also, the step of detaching the battery connector is optional, but honestly, it only takes a second (definitely use a plastic spudger or other non-conducting, non-scratching tool) and an accidental electrical short can cause some very expensive damage to circuit boards - really, just always do it.