Upgrade App to Lightning
You can upgrade a Classic app to a Lightning app in Lightning Experience, enhancing it for your Lightning Experience users with a customized color, logo, utility bar, and additional items like Lightning pages supported in the navigation bar.
To Upgrade your App to Lighting follow the below mentioned steps,
Your Classic app is copied and upgraded for Lightning Experience. You now have two versions of the app:
After you upgrade it, the Classic app is no longer accessible in Lightning Experience via the App Launcher. You’ll still see the Classic app in the apps list, but with the Visible in Lightning column deselected.
The two versions of your app now must be managed separately. Future changes you make to the Classic app won’t be reflected in the Lightning version of the app, and vice versa.