I'm looking for instructions that explain how to update from the J4 template to the J5 template
without having to reinstall my Joomla..
Can you send me instructions/video on this?
If you're using our templates, you can simply use JA Extensions manager component to update the new version of template: https://www.joomlart.com/update-steps
In case that you're using a custom template which built with T4 framework, I'm afraid that you have to check the compatibility directly with Joomla 5 and update files/layout if needed.