Hello,
You need to make the full backup and update the theme on your site, then you will find the list of plugins to update in the Install Plugins in Appearance. Deactivate and delete CMB2 and Redux plugins, they are no more needed.
I would recommend you to arrange a staging site and install a new WordPress installation.
Install the theme and upload the demo (if you want demo) then, recreate the header in the Header builder: https://xtemos.com/docs/woodmart/header-builder/ you can try export-import header from your live site to the testing: https://xtemos.com/docs/woodmart/header-builder/how-to-exportimport-headers/
Then recreate or migrate the footer and all the widgets area. As soon as you finish the site configuration, delete all the demo, and import-export the content from you live site.
Finally, you can add the other plugins from the live site one by one checking the site. Then as soon as the site is ready you can move it to the live site.
Updating the theme in the live site would crash part of the site and you will have to recreate some parts of the site in any case.
If you have any questions please feel free to contact us.
Best Regards
.
