Sadly, you can not upgrade the hard drive in the traditional sense. In fact, this Chromebook does not even have a hard drive installed. It uses something called an eMMC. This is a flash storage card that is soldered onto the motherboard. It’s similar in size and shape to an SD card, but is closer in function to a solid state drive.
While the eMMC in the Chromebook is only 16gb, you can offset the small storage capacity by using [https://www.google.com/drive/|Google Drive]. The Asus Chromebook C201 comes with 100GB of free cloud storage for 2 years.