I am trying to change my oralce8i 8.1.7 installation on W2000 server character set from 'WE8ISO8859P1' to 'UTF8' when I am running 'alter database character set UTF8;' I am getting following error

alter database character set UTF8
ERROR at line 1:
ORA-12712: new character set must be a superset of old character set.

But I need to change to UTF8. How can I do this?

Could someone help me please