The first thing I would recommend is to use a can of air. It is probably the safest way to clean a keyboard, but is mainly used for crumbs or dust. If it’s sticky, you can use a LCD screen cleaner, and spray the key and let it soak for a few minutes. Then, use a can of compressed air to blow the excess screen cleaner out from under the keys.
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 Google Drive. The Asus Chromebook C201 comes with 100GB of free cloud storage for 2 years.