Hello Luthango,
The reason we recommend backing up the configuration is not only for upgrades but to protect yourself from any unpredictable issues during the process. The configuration is separate to the OS and will be loaded after the reboot on the new image automatically. You can treat the stacks the same considering the master node will propagate the image to the rest of the nodes.
In the future I would recommend making a new post for any questions or issue. This way everyone in the community will be notified instead of just the people who have responded to this post.