RMAN - need to delete all backups

I am out of space from backup but not able to delete all backups. Seems all obselete files are all gone. How can I delete all backups so I can get the space back?
here are some examples:
RMAN> crosscheck backup;
using channel ORA_DISK_1
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_19/annnf0_daily_incremental_0.385.612253303 recid=2930 stamp=612253302
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=/home/oracle/backup/RRSDEV/c-2299215697-20070119-00 recid=2931 stamp=612253304
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_20/annnf0_daily_incremental_0.276.612338407 recid=2932 stamp=612338407
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_21/annnf0_daily_incremental_0.1098.612424805 recid=2933 stamp=612424805
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_22/annnf0_daily_incremental_0.1064.612511207 recid=2934 stamp=612511207
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_23/annnf0_daily_incremental_0.400.612597607 recid=2935 stamp=612597606
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_24/annnf0_daily_incremental_0.391.612684007 recid=2936 stamp=612684007
crosschecked backup piece: found to be 'AVAILABLE'
backup piece handle=+DG2/rrsdev/backupset/2007_01_25/annnf0_daily_incremental_0.351.612770409 recid=2937 stamp=612770408
crosschecked backup piece: found to be 'AVAILABLE'

delete backup;

It works. What if I need to delete subset of these next time? Can I just delete certain month?