WordPress 2.7 has added some new features that help automate the upgrade process for the core WordPress files as well as plugins (which got a 1 click update previously).
These are handy features. We do WordPress upgrades for a lot of clients, and to avoid upgrade glitches here are some things that are useful to do well before applying the upgrade.
1. Review the changes and the impact they will have
Go through the release notes for the upgrade or patch and see what is changing. What will be the impact on Dashboard users and site visitors? Do you need to let anyone know before things change?
2. Look for dependencies
Does anything else depend on something that is changing? If WordPress is removing a hook that is used by your theme or a plugin, it helps to identify this upfront so you can prepare for it.
3. Upgrade themes and plugins to take advantage of new features
Most WordPress upgrades introduce new features, and many of these require changes to themes and plugins to take advantage of. For example, here is the list of changes recommended to upgrade to WordPress 2.7. You need to be particularly careful if you have customised theme files.
4. Test
Even the best laid plans can go astray, so do the upgrade on a test version of your website and check the upgrade goes smoothly. Check your server logs to make sure you don’t have any new errors appearing, and if you have a high volume website, you may want to run performance tests that compare before/after results.
5. Now you can upgrade!
Running your upgrades after you have assessed impacts, checked dependencies, made required code changes and completed testing should reduce the chance of having an unexpected glitch after your update.
You should have a full backup of your site before you upgrade, and an understanding of how to restore from that backup if you need to.