Upgrading 13' Macbook Pro Late 2011

So i have noticed my Late 2011 Macbook pro 13' has slowed down since i upgraded to Yosemite. I bought the base which has 4 gb of ram and a 2.4 ghz intel core i5. From all the suggestions i've been told to upgrade the ram and change to a ssd. Im wanting to upgrade the ram first as its cheaper and it might solve the problem. I have no idea what brands are good for ram so this is what i need help with. Also is it preferred that i take it to a professional?

Thanks