To secure the server its always preferable to disable the telnet service. To disable the Telnet login in to the server as a root user and follow the steps.
Open the telnet configuration file with the favorite editor
Change the parameter
disable = no
disable = yes
Save and Exit the /etc/xinetd.d/telnet file
Now restart the telnet service , so that new configuration will load with the telnet service.
Now try to telnet to the server ip to confirm the telnet disabled or not.