Renaming an Instance

Query to see the current instance name:- 

sys>>select instance_name from v$instance;

sys>>shut immediate

Edit the environment variable "ORACLE_SID" with 

the <new SID>:-

oracle@localhost ~]$vi .bash_profile

export ORACLE_SID=<new SID>

:wq

Run the ".bash_profile" file:-
oracle@localhost ~]. .bash_profile
 

Display the <new SID>:-
oracle@localhost ~]echo $ORACLE_SID
<new SID>

Now copy the old init<$ORACLE_SID>.ora with 

new init<$ORACLE_SID>.ora:-
oracle@localhost ~]cd $ORACLE_HOME/dbs
oracle@localhost dbs]cp init<oldSID>.ora init$ORACLE_SID.ora
oracle@localhost ~]sqlplus / as sysdba

sys>>startup

Now check the instance name with the following query:-
sys>>select instance_name from v$instance;