You can remove a sandbox when you no longer require the testing environment.
To retain data from the sandbox, you can first export the data to a CSV file and later import it to a different environment. For information about the import/export feature, see Importing and Exporting Data.
To remove a sandbox:
Select the checkbox of the sandbox you want to remove.
Click … > Delete or Actions > Delete.
The sandbox is removed as soon as you click Delete. All users being added to the sandbox will also be removed (except for users added outside of the sandbox). In addition, ensure that you refresh your browser for the deleted sandbox to be removed from the user account menu, located at the bottom of the left navigation bar of the Cloud Services Portal.