Unfortunately once the new version is installed there is no way for you to roll back. The only way you can get back to the old one is if you already have a copy of, or can manage to find the APK file for the version that you want. To be pedantic, you can uninstall updates for System apps.

How do I uninstall the latest Android update?

Go to device Settings>Apps and select the app in which you want to uninstall updates. If it is a system app, and no UNINSTALL option is available, choose DISABLE. You will be prompted to uninstall all updates to the app and replace the app with the factory version which shipped on the device.

How do I go back to previous Android update?

Once you have tapped on the app, it then opens a new screen where you will find the button ‘Uninstall Updates’, which you need to select. This will uninstall all updates to this Android system app. After doing this, the app will be revert back to its original state.