Drop the database:

With dbca:

Launch dbca: [oracle@ORAVM1 dbhome_1]$ dbca

Choose “Delete a Database” and click Next:

Select the database that you want to delete and click Next:
 

Confirm that you want to delete the database:

Click No to stop DBCA:

Manually with the DROP DATABASE statement:

export ORACLE_SID=ocmdb1

sqlplus / as sysdba

SQL> shutdown immediate
SQL> startup mount exclusive restrict
SQL> drop database;