You can access your App Settings via Setup Home by clicking on the cog at the bottom left of your navigation bar. From Setup Home, scroll down to the bottom to find App Settings.
From your app settings, you can:
Rename your app (change the name that appears in the app bar and the top of the navigation bar)
Change your app's URL
Delete your app
Grant Support Access (when prompted, tick this box to allow customer support to help)
Connect a custom domain
Request an upgrade on your cache frequency (the standard is 15 minutes but we can reduce this to 5 minutes)
Set your default table permissions
Add Custom Scripts
App appearance (Here you can update the choices you made when you created the app - the icon and colour theme.)
Menu Settings (Here you can change what and how layouts appear in your navigation bar.
You can rename layouts by clicking on the pencil icon, reorder them by dragging, toggle them on or off and set which Roles have access to them by clicking the globe)