In Kerberos 5, you don't :-)

There currently is no way to rename a principal using the MIT V5 admin
system (even though the man page for kadmin claims otherwise).

The issue is that in Kerberos 5, the key is salted using the full principal
name, so changing the principal name would invalidate the user's password.
However, since the Kerberos database provides the ability to store an
alternate key salt, this could actually be implemented.

The current workaround is to simply delete the old principal name and create
the new principal name.