ORACLE - Kill session

You plan to work on a schema or to drop a schema and Oracle throws you a warning saying Schema is in use. What do you do?

SQL> select sid, serial# from v$session where username='{your-schema}';

Please observe the sid, serial# from the output, then proceed to kill the session with 

SQL> alter system kill session 'sid,serial#';

You can rerun the select statement again to verify the specific schema has been removed.