Size of Flash Recovery Area and a new DB_UNIQUE_NAME

How can I clean up the Flash Recovery Area  (Oracle 11gR1 on Windows2008)? 

After  DB_UNIQUE_NAME changed from myOld to myNew,

under %Oracle_Home%/flash_recovery_area, there were two folders, myOld and myNew.

By OS level, I deleted all files on myOld and myNew I did not need.

On RMAN

crosscheck backupset;
delete noprompt expired backupset;

crosscheck archivelog all;
delete noprompt expired archivelog all;

crosscheck backup;
delete noprompt expired backup;

However, the freeSize or space_used on v$flash_recovery_area_usage and v$recovery_file_dest were Unchsnged.

Thank you for help

Liz