-- To delete all backups for the target database use:

RMAN> DELETE BACKUP;

-- Delete Backupset, to delete a backup set specify the set number e.g. 15:

RMAN> DELETE BACKUPSET 15;

-- using TAG:
delete backup tag = 'INCR LEVEL 0 DB';

-- delete old completed backups
delete backup completed before 'sysdate -7';

-- using RECOVERY window:
DELETE NOPROMPT OBSOLETE RECOVERY WINDOW OF 7 DAYS;

--NOPROMPT keyword
By default the DELETE command will prompt for confirmation before deleting any backup files

Do you really want to delete the above objects (enter YES or NO)?
To suppress the prompt specify the NOPROMPT keyword. For example:

RMAN> DELETE NOPROMPT BACKUP;

--Expired Backups
To delete any expired backups detected by the CROSSCHECK command use:

RMAN> DELETE EXPIRED BACKUP;
To delete all expired archive logs detected by the CROSSCHECK command use:

RMAN> DELETE EXPIRED ARCHIVELOG ALL;

--Obsolete Backups
To delete backups that have become obsolete based on the retention policy.

RMAN> DELETE OBSOLETE;