Usually you would do this to allow the retention of more archivelog.
ALTER SYSTEM set db_recovery_file_dest_size=120G scope=both;
cd into the archivelog subdirectory – then to purge archivelogs to both these things
1st remove all archivelog older than 4 days – don’t do either of these commands if you need this archive
find . -mtime +4 -exec rm {} \;
/bin/find /u01/app/oracle/fast_recovery_area/PROD/archivelog -type d -mtime +7 | xargs rm -rf rman target / <<EOF crosscheck archivelog all; delete noprompt expired archivelog all; EOF