Use APKPure App
Get Update To Android 7 old version APK for Android
Update your old rooted device to Android 7.
Do you want to switch to version 7 of Android ? It is very simple.
If you have an older device that has a previous version of Android than version 7 and your device is rooted, you can use this app to upgrade your rooted device to Android 7.
This application requires root permission.