Jenkins, by default, runs on port number 8080. For changing the existing port from 8080 to the desired port number, we can take the following steps:
Run Jenkins using the command line
Execute the command, java -jar -httpPort=desired_port jenkins.war
If Jenkins is installed using the Windows package, then:
Go to Program Files/Jenkins directory
Open Jenkins.xml in the editor
Find --httpPort=8080 and replace the port 8080 with the new port number