Hello! I bought a 13" Retina Macbook pro earlier this year and I think I'm at a point now where I need to put some more memory in. My computer's current specs are: Processor: 2.6 Ghz Intel Core i5 Memory: 8 GB 1600 MHz DDR3 Graphics: Intel Iris 1536 MB Version: 10.10.4 Yosemite I was thinking about ordering this from Amazon but I had a couple questions before I did that: Would I have to replace all of the RAM currently in my machine or could I just add on to it? Are there any other options that users here would recommend other than this one? Is this a good deal? Thanks!