I don't believe that CCP supports resizing the root volume. Since root volume size is determined by the template, getting this to work would potentially break the ability to reset the instance to the original template.

What I'm about to suggest wouldn't be supported and should be tested with another Instance before trying it on the desired Instance. Please note, I haven't tried this myself but it might work.

1. Create a test instance using the same template
2. Login to test instance to verify everything works
3. Shutdown the test instance
4. In XenCenter, find the volume associated with the test instance (will need the UUID of the volume, I think)
5. Resize the test instance's disk
6. Start the test instance
7. Login to test instance and resize the filesystem (and volume if template uses LVM)

If step 6 doesn't work, you may need to modify the CCP database (unsupported) to mark the root volume as a different size. This will likely be needed anyway if you are "billing" for storage.

Good luck and let us know how it goes.

--Mike@Redapt