How to upgrade from ROS2 Foxy to Humble or Galactic without losing data?

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I am using Gazebo Ignition Citadel (debian install), Ubuntu 20.04, VMware 16.04, ROS2 Foxy (debian install), Rviz2 Since I didn't have enough points I have to attach the links of google drive for the image.

I am trying to create a map of the environment. I am using the igt_ignition package of this github repo ( https://github.com/TechnoYantra/ros2-igt) . I am not using nav package since I am using a dockerised version of slam_toolbox.

This is what my tf tree looks like. https://drive.google.com/file/d/1yd_M...

Whenever I try to add the map topic in the rviz2. RViz2 throws this error. https://drive.google.com/file/d/1mP_H...

On the Rviz screen it is just one frame of map https://drive.google.com/file/d/1Lzzp...

Based on this link, (https://bytemeta.vip/repo/ros2/rviz/i...) I should upgrade the ROS to galactic or humble.

Question

So, I wanted to ask this question, how should I change my ros distro from Foxy to Galactic or Humble without losing any data?

Optional question, if any one has any idea how to fix this error with ROS2 Foxy only, that would be great?

Lastly, can someone tell me what are some of the debugging tools to verify there is no other TF frames based issue?

NOTE: If more information is needed let me know