Steps To Change DBNAME DBID

To reset the DBID and DBNAME, here are some top level steps

• alter system set cluster_database=false scope=spfile;
• shutdown immediate;
• startup mount;
• exit;
• nid TARGET=SYS  DBNAME="your DB Unique Name"
• sqlplus / as sysdba
• create pfile=’dbid_pfile.ora’ from spfile ='spfile_dbname.ora';
• exit;
• Edit  dbid_pfile.ora
• SET *.db_name parameter =’ <DB_UNIQUE_NAME>’
• SET *.cluster_database=true
• Save your changes.
• sqlplus / as sysdba
• create spfile ='spfile_dbname_new.ora' from pfile=’dbid_pfile.ora’;
• startup mount;
• alter database open resetlogs;

Refer :  http://docs.oracle.com/cd/B28359_01/server.111/b28319/dbnewid.htm