Duplicate database

My company is using oracle 7.3.4 on AIX. I am trying to duplicate the database - ACDB by copying the datafile to another hardisk,
then I used the trace file which created earlier to create the new instance - NEWDB.
The database is up and running, as ORACLE SID is NEWDB, but the global name is still as ACDB.

Do I miss out any steps, or it's there anywhere to change the global name.

Thank you
Gavin

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