Take a full backup of your database before applying the change.

change the NLS_CHARACTERSET from WE8MSWIN1252 to AL32UTF8;

select * from NLS_DATABASE_PARAMETERS where parameter=’NLS_CHARACTERSET’;

PARAMETER                      VALUE

NLS_CHARACTERSET               WE8MSWIN1252

Change the database character set perform the following steps as sys user

shutdown immediate

startup restrict

alter database character set AL32UTF8;

if error do below

alter database character set INTERNAL_USE AL32UTF8;

shutdown immediate

startup

Check the new version

select * from NLS_DATABASE_PARAMETERS where parameter=’NLS_CHARACTERSET’;

PARAMETER                      VALUE

NLS_CHARACTERSET               AL32UTF8