It's very easy. Just unscrew about 8 screws I think, and the cover comes right off. Make sure to touch something metal first though so as to eliminate static charge before you change RAM. Once the cover is removed, you will see the battery, a few other things and at the bottom, both RAM sticks.
Just to clarify, when you are ready to put the new sticks in, you have to sort of slide them in their slot first and then push down slightly for them to fit in place. Might seem odd or even scary (thought of broken sticks 😛) but ya, it's done that way.
Really straightforward. There are a lot of youtube videos on this but I personally find it a waste of time to watch - they take 15min to explain a 5 min procedure!
Good luck!