In theory, all the intermediate upgrades will be applied. Some of this is overkill, but since it is such a big jump, I would do the following before the upgrade (in this order):
- Back up the site (both files and database)
- Turn off the FURL, compress_css, and compress_js System Settings
- Rename .htaccess
- Clear the manager and error logs
- Disable all plugins (by right-clicking on them in the tree and selecting "Deactivate Plugin")
- Clear the site cache
- Flush permissions
- Flush all sessions
After the upgrade (before logging in):
- Delete all files in the core/cache directory
- Clear your browser cache and cookies
Also, see the method here for transferring the updated MODX files:
http://bobsguides.com/modx-upgrade-faq.html
