Finding a reliable download for older firmware can be tricky. Here are the primary ways to secure the official or stable update files:

Upgrading from Marshmallow to Nougat on your Oppo F3 brings several noticeable improvements:

More icons and easier customization in the pull-down menu. How to Install the Update Manually

A built-in blue light filter (Amber light) to reduce eye strain at night.

If the official link is unavailable for your specific region, community-vetted mirrors like Google Drive archives for Android 7.1.1 are often used by enthusiasts.

For those comfortable with advanced modifications, LineageOS Downloads offers unofficial builds of Android 7.1 (LineageOS 14.1) which provide a "stock" Android experience without the ColorOS skin. Key Features of the Nougat Update