How to change the app title in a UWP app

Try this:

var appView = Windows.UI.ViewManagement.ApplicationView.GetForCurrentView();
appView.Title = "Your title...";

Current accepted answer modifies the View title, not the App title. That appears to be good enough for the OP but if you want to actually change the App Title for a UWP app, here's what you do.

Open your package manifest and navigate to the "Application" tab. You'll see the app's display name like so,

Then just change the "Display name:" field to whatever you want your custom app title to be, then re-build and you're good to go, like below,