Agent Contact Method is one of three ways (Configuration <> Server Settings <> Agent Contact Method - order can be rearrange to fit your environment):
1) Fully Qualified Domain Name
2) NetBIOS Name
3) IP Address
Perhaps after renaming the endpoint schedule a reboot for that endpoint.
I did this and reorder it but it is not fixed, When I rename my system in system tree it is not transfer in epo and the communication for update task is broken. what should I do?
Do you receive the same results after rebooting the endpoint?
How are you renaming the systems? Are you able to ping/tracert to the FQDN of your ePO server?