Hello.

We have very old servers with stats. Our data center change ip network and our server have new ip address. Old ip is down.

Can I just change IP address of my claimed servers?

For example:
http://www.gametracker.com/server_info/91.194.73.60:28950/
http://www.gametracker.com/server_info/91.194.73.60:28960/
http://www.gametracker.com/server_info/91.194.73.60:28980/

Old IP (currently not working): 91.194.73.60
New IP (worked): 185.4.41.60

Thanks.

You would be able to accomplish an IP change, assuming the ports remain the same, by making use of the DNS feature. You can enter your DNS on the page you claimed the server on. Simply enter the DNS you have setup, save, and when you want to switch it over, point the DNS to the new IP and wait for GT to switch it over.