Delete old partitions (not required for most)
If you installed Linux with my old instruction guide (http://raywaldo.com/2013/01/howto-ubuntu-on-chromebook/) you will need to manually delete the Linux partitions from your hard drive before proceeding. If you do not, then you will only have access to the partition that you allowed ChromeOS to own.
I do not have a guide to do this but this method should work well:
1. First pull the drive and attach it to another Linux computer. Then use the GParted package to delete the partitions and create a new one that you would format to Fat32, as if it were a new drive.
2. Then, you will need to rebuild the ChromeBook OS. Follow the guide from the ChromeBook help site here: https://support.google.com/chromebook/answer/1080595?hl=en