First you must open your computer. In most scenarios the computer will not be larger than you and you should not have any problems.
Next, you may have to remove some other components if they are blocking the way. In this case the video card is blocking access to the RAM. Remember, it looks tasty but don't eat it.
Finally, you will have access to the precious RAM. Simply pull on it really hard, you may need a hammer, and out it comes. Remember, don't eat it.
If you simply cannot resist the RAM's siren call to take a nibble then try to taste a corner
However, it will make you throw up.