Updating stock ROM Android 5.1 to newer Android? Hi8 pro

Hi bros! I hope you can help me on the subject. Have the duaboot version, tablet is still going great but I want to flash a newer version of Android on it for compatibility issues (newer app not working with 5.1)

I have checked threads and tutorial ([Hi8 Pro] [Tutorial] How to flash Android for Chuwi Hi8 Pro)… it seems I could flash ROM provided (no warnings to worry) but it’s not what I need since everything is working fine (despite the compatibility issue).

There is an option of “update” instead of “recover” but I understand I should have the newer Android ROM available on disk.

Thanks in advance for your help.