For changing Tomcat port you need to change the connection port in server.xml :
sudo vim /etc/tomcat8/server.xml
Then search for “Connector port” and change the port number (example 8080 to 7000):
Connector port="7000" protocol="HTTP/1.1"
connectionTimeout="20000"
redirectPort="8443" />
In example above we change the port from 8080 to 7000
Then you need to restart tomcat :
sudo service tomcat8 restart