How to change National character set from UTF8 or any in 11g

sqlplus / as sysdba
STARTUP MOUNT exclusive RESTRICT
ALTER SYSTEM ENABLE RESTRICTED SESSION; 
ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0; 
ALTER SYSTEM SET AQ_TM_PROCESSES=0; 
ALTER DATABASE OPEN ;
update props$ 
set value$=' WE8ISO8859P1' 
where name in ('NLS_CHARACTERSET', 'NLS_NCHAR_CHARACTERSET'); 
commit;
SHUTDOWN IMMEDIATE;