MacBook Air owners can’t upgrade many parts of their laptop, but tech-accessory maker Transcend offers storage upgrade kits that cost far less than a new Mac.
These kits include an SSD (Solid State Storage) module, two screwdrivers, and an SSD enclosure. The inclusion of the screwdrivers and enclosure make this kit easy to recommend because it shows Transcend was thinking ahead. Opening a MacBook Air is difficult because Apple uses uncommon screws, and most people don’t have the right tools.
The drive enclosure, which looks like a flash drive with a USB port on it, serves two functions. The first is to hold your new SSD, so you can easily connect it to your computer and transfer all of your data. Once you’ve installed your new SSD, you can keep your old one in the enclosure and use it as external storage.
They may not be cheap, but these drives should help you get an extra couple of years out your current machine.
See http://www.businessinsider.com/transcend-jetdrive-macbook-air-storage-space-solution-2017-5#-/ 
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