1. Open the file jenkins.xml from the location where Jenkins was installed (e.g. C:\Program Files (x86)\Jenkins).
  2. Search for httpPort and updated it with whatever you wanted it to be (e.g. 9080) as long as it doesn't introduce any conflicts.

    Example update to 9080

    <arguments>-Xrs -Xmx256m -Dhudson.lifecycle=hudson.lifecycle.WindowsServiceLifecycle -jar "%BASE%\jenkins.war" --httpPort=9080 --webroot="%BASE%\war"</arguments>