RMAN> delete archivelog all;
released channel: ORA_DISK_1
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=128 instance=primdb1 device type=DISK
RMAN-08137: WARNING: archived log not deleted, needed for standby or upstream capture process
archived log file name=+DATA/primdb/archivelog/2013_01_19/thread_1_seq_78.1103.805122453 thread=1 sequence=78
RMAN-08137: WARNING: archived log not deleted, needed for standby or upstream capture process
archived log file name=+DATA/primdb/archivelog/2013_01_25/thread_1_seq_79.1104.805643747 thread=1 sequence=79
...
List of Archived Log Copies for database with db_unique_name PRIMDB
=====================================================================
Key Thrd Seq S Low Time
------- ---- ------- - ---------
1 1 4 A 29-OCT-12
Name: +DATA/compdb/archive/1_4_797940996.arc
4 1 5 A 29-OCT-12
Name: +DATA/compdb/archive/1_5_797940996.arc
...
275 2 72 A 19-JAN-13
Name: +DATA/primdb/archivelog/2013_01_19/thread_2_seq_72.1101.805122423
276 2 73 A 19-JAN-13
Name: +DATA/primdb/archivelog/2013_01_19/thread_2_seq_73.1102.805122443
Do you really want to delete the above objects (enter YES or NO)?
...
Sometimes, there could be some reasons to prevent you from deleting the archivelogs, you still can delete them forcibly by adding a keyword FORCE.
RMAN> delete force archivelog all;
released channel: ORA_DISK_1
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=128 instance=primdb1 device type=DISK
List of Archived Log Copies for database with db_unique_name PRIMDB
=====================================================================
Key Thrd Seq S Low Time
------- ---- ------- - ---------
1 1 4 A 29-OCT-12
Name: +DATA/compdb/archive/1_4_797940996.arc
4 1 5 A 29-OCT-12
Name: +DATA/compdb/archive/1_5_797940996.arc
...
285 2 76 A 25-JAN-13
Name: +DATA/primdb/archivelog/2013_01_25/thread_2_seq_76.1108.805644053
286 2 77 A 25-JAN-13
Name: +DATA/primdb/archivelog/2013_01_25/thread_2_seq_77.1109.805644059
Do you really want to delete the above objects (enter YES or NO)? yes
...