For server, it's in the general configuration.
For Cloud, you can't.
In both cases, the base url must match the url upon which your users are using JIRA. You can't change the url for Cloud, so you have no need to change the base url (ok, you can, but technically, that's "copy old site to new one and delete the old site", not a simple change)
The doc you've referred to is about naming your application, not the url it runs on. By default, JIRA is called JIRA, but there's no harm in calling it "Bob" or "My issue tracker" or "Slartibartfast" if you feel like it.
Hey Community mates! Claire here from the Software Product Marketing team. We all know software development changes rapidly, and it's often tough to keep up. But from our research, we've found the h...
Connect with like-minded Atlassian users at free events near you!Find a group
Connect with like-minded Atlassian users at free events near you!
Unfortunately there are no AUG chapters near you at the moment.Start an AUG
You're one step closer to meeting fellow Atlassian users at your local meet up. Learn more about AUGs