Here is how to drop a database in Oracle.
Make sure that have ORACLE_SID set first.
Log into sqlplus with sysdba privileges:
sqlplus /nolog connect / as sysdba
Run the following commands in sqlplus:
shutdown immediate startup restrict mount exclusive
Before you complete the drop, verify that you are in the correct database — the one that you want to drop (thanks to Dan Norris’ comment):
select * from v$database;
Now you can drop the database.