How to change NLS_CHARACTERSET to AL32UTF8

Below are steps:

SQL> SHUTDOWN IMMEDIATE;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> STARTUP RESTRICT;
ORACLE instance started.

Total System Global Area 6.0663E+10 bytes
Fixed Size                  2268032 bytes
Variable Size            5637145728 bytes
Database Buffers         5.4895E+10 bytes
Redo Buffers              128344064 bytes
Database mounted.
Database opened.
SQL> ALTER SYSTEM SET JOB_QUEUE_PROCESSES=0;

System altered.

SQL> ALTER SYSTEM SET AQ_TM_PROCESSES=0;

System altered.

SQL> ALTER DATABASE CHARACTER SET AL32UTF8;

Database altered.