Like web3.personal.lockAccount() and web3.personal.newAccount() is there any method available or any other API's exist to update account passphrase over RPC?
The JSON RPC does not include any methods for updating your password.
Even using the
geth command, you can only update your account password interactively. From Managing your accounts - Updating an existing account:
Since only one password can be given, only format update can be performed, changing your password is only possible interactively.