@macmanx is exactly right. I just started with a new client last week and they were still on 2.6. Here were my steps:
- Got a full backup of all files and database.
- Took the site out of production..(!Important)
- Reviewed the functions.php file for any obvious conflicts between 2.6 and 2.92.
- Copied the .htaccess file
- Made notes of any plugins that were no longer compatible with 2.92 and uninstalled them. (there was an old SEO plugin and a events plugin that were no longer supported) With the events plugin I exported the data so I could import it into the new plugin.
- Copied all settings from current plugins (screen shots and notes)and widgets (there were 20 text widgets with custom code (adds and pictures)...a real pain)
- There were 22 plugins that required upgrade...I decided to wait until the WP Core was updated before upgrading the plugins.
- Did a manual upgrade to 2.8 and upgraded to 2.92 with the automated update system.
- Got another backup of the database just to be sure.
- Upgraded and activated all plugins.
- Reset their environment
- Got one final backup of the database before launch.