Changing the title does not change the web address (URL) of the app. If having the title match the URL is important, or less confusing to your team, consider re-creating a new app with the desired title and deleting the old one. Of course, this works better early in the process, before you upload documents or create apps!
If you already have many items in your app, you can copy documents from one Library app to another, or export an existing List app to Excel and re-import into a new one. However, this shouldn't be taken lightly. Some column configuration settings, such as a Choice column, need to be re-created along with many other app settings. If you’re unsure what you want to name an app when you create it, take some time to consider your terminology before creating the app.