The network administrator must change the VTY line configuration so that it only accepts SSH and no longer accepts Telnet. The required change is to modify the transport input command to allow only SSH.

On Cisco switches, this is done under the VTY lines, for example:

text

Switch1(config)# line vty 0 15
Switch1(config-line)# transport input ssh

This replaces the usual default such as transport input all or transport input telnet ssh, which would still permit Telnet.

So, the correct answer in exam-style wording is:

Modify the transport input command (change it so it reads transport input ssh).