Removing locks in Oracle without being admin
If this happens often there is an option to write a package or a stored procedure for that. The owner of the package would need the alter system privilege and the package should be created with definers rights.
You just need execute privileges on that package and feed the session kill procedure with the right parameters.
There is still a good chance that zombie processes keep running until the end user that was running the killed processes tries to do anything. These zombies kan be killed from the OS. To find those processed, before killing read their os pids by joining v$session with v$process. An other option is to regularly clean those orphaned processes by finding processes in v$process that have no session in v$session.