add / create redo logs

use the following to view current redo log file information
select * from v$log ;

use the following to drop a redo log (if required)
alter database drop logfile group ...

use the following to add a new redo log
alter database add logfile group ... '...' size ...m reuse;

when trying to drop a logfile the following error occurs

ERROR at line 1:ORA-01624: log 2 needed for crash recovery of instance CSHMNT
ORA-00312: online log 2 thread 1: '/db/cshmnt/redolog/001/redo02.log'

Try : alter system checkpoint
This should checkpoint the database and make all redolog files INACTIVE, allowing to drop redo log files.

log_buffer

Consider increasing the log_buffer database parameter if the following two system statistics are noticably abover zero.

SELECT name, value from SYS.v_$sysstat
WHERE NAME in
('redo buffer allocation retries','redo log space wait time');

These statistics are cumulative since database startup.