I have a Toshiba Satellite Model C55-B5382 laptop computer that I wish to upgrade from 4 GB to 8 GB RAM. I looked on youtube and doing the upgrade looks pretty simple. The problem I'm having is identifying the RAM HW chip/card to buy. From looking at the youtube video it appears I need to purchase an 8 GB RAM chip/card and replace the 4 GB chip that is currently in my laptop (one cannot buy a 4 GB chip/card and add it to the existing chip/card in my computer). Is this correct? Also, I need to know the basic characteristics I need to consider when purchasing the new RAM chip/card. There are many products on the market and it would be easy to make a selection that doesn't work for my computer.