I did this with my 2011 13 inch, the job is a 5 min job, however note this: Get a good screwdriver, a REALLY good one that fits perfectly, you don't want to be striping screws or scratching them up,it's worth it your your everyday as well.
Be careful to just touch the board of the ram, not the contacts or the Macbook's motherboard, don't want to zap anything.
Some screws are diffrent and all are locktighted, beprepaired to use just enogh force and such, I found the lock tight that remains on the screws tends to make them want to only work in the hole they came out of.
Make sure the mac is fully powered off.
If you follow this, your total costs would be under $75. Heck with the money you save, you can go Optibay at the same time with an SSD.