[oracle@primary01 ~]$ sqlplus / as sysdba
...
SQL> show parameter db_recovery_file_dest_size;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest_size big integer 20G
SQL> alter system set db_recovery_file_dest_size=40G scope=both;
System altered.
SQL> show parameter db_recovery_file_dest_size;
NAME TYPE VALUE
------------------------------------ ----------- ------------------------------
db_recovery_file_dest_size big integer 40G
Upsizing the space of FRA is an easy way to get you out of the trouble when FRA is full, but you should consider available space of your storage. Since the overall space of storage is not infinite, it's impossible to add space to FRA every time you are stuck in the same problem. The best practice is back to RMAN to manage the space.