Kill sessions in Oracle

How to kill a running session in Oracle?

 SELECT 'exec sys.kill_session(' || sesion.sid || ',' || sesion.serial# || ');', sql_text  
 from v$sqltext sqltext, v$session sesion  
 where sesion.sql_hash_value = sqltext.hash_value  
 and sesion.sql_address = sqltext.address  
 and sesion.username is not null  
 order by sqltext.piece;