I don’t exactly know if Chromebook users have to take care of special, but if I would want to (re-)install a Linux distribution, I would just clean the part of the disk that I need, format that part and then cleanly install the distribution onto that part. That is basically it. No need to uninstall or remove anything, as long as you format it.
To do what I mean in a simple way, just check out how to install a distribution onto a computer. If Chromebook has a disk, it should work pretty much the same way. In the second worst case scenario you would need to extract the storage medium from the device and install the system from another computer onto this disk. Not even this operation would be that hard, though.