Crucial does a good job of letting you know what's in your laptop before you crack it open and realize you've bought the wrong hardware. (They only list their own products as expected, so you'll have to browse options elsewhere.)
I see that you have one single memory slot and a maximum of 8GB supported, so you'll want to purchase an 8GB stick to replace the current one. I found a couple nice options
here and
here. The only difference is in brand. They also satisfy the 1.35V requirement mentioned in Dusty's post.
Be sure to watch a video of someone removing and replacing the modules before doing it yourself for the first time!