Yes, you can easily deactivate a tablet that you no longer wish to use.
To deactivate your old tablet:
1. Log into the Ocean portal.
2. Navigate to the Tablets tab.
3. Find the tablet(s) that you would like to deactivate, click on it and select "De-register". The tablet(s) has now been deactivated.
To set up your new tablet:
1. Follow the usual steps to set up Ocean on your tablet (please see here for detailed instructions).
2. Log in to the Ocean portal.
3. Navigate to the Tablets tab.
4. Ensure that your newly set-up tablet is under the right settings group in the Ocean portal. New tablets are automatically added to the "Default" settings group. If you want to change this, drag and drop the new tablet into the correct tablet group.