Locate the downloaded APK and tap install. The app will request permissions to display over other apps (for the floating widget) and access to your storage.
Software updates are not always improvements. The developer community around x8 Speeder has released many versions, but 3.3.6.4 holds a legendary status for several reasons: x8 speeder 3.3.6.4
Once you clarify which one you're interested in, I'd be happy to share the story or more details about it! Locate the downloaded APK and tap install