From DB machine Home Page, select Database Machine, then selecting Provisioning, then click Scale down cluster.
Select the Cluster to scale down. Once selected the list of DB zones in the Cluster appear.
Select the Solaris Zones to delete
Provide Solaris zone Host credentials for the Oracle Home (oracle user)
Provide Solaris zone Host root credentials
Provide Exadata Storage Server Credentials
Provide Database Domains host root credentials