I’ve successfully migrated two WordPress 2.9 blogs to WordPress 3.0. No issues. Here are steps to follow to do so safely:
Phase 1: Backup
- Click on Tools > Export. The “Export” page is displayed.
- Click the Download Export File button. A “Save as” dialog is displayed. Save the file on your desktop.
- Click on Dashboard. Note the version of WordPress that you are running. The version number is near the bottom of the “Right Now” box.
Note that this will not backup plugins or themes. For a more complete backup, also FTP to your webhost and download everything in your blog’s folder.
Phase 2: Upgrade
- Click the Please update now link that’s at the top of all your WordPress admin pages. Alternatively, go to your dashboard, and click the Update to 3.0 button that’s displayed in the “Right Now” box. The “Upgrade WordPress” page is displayed.
- Click the Upgrade Automatically button.
- Wait a few moments, until the text “Upgrade completed successfully” is displayed on the page.
You’re done! Click around to make sure everything works okay. View your blog to ensure that it still displays properly.
Phase 3: If Everything Goes
If your blog is somehow borked as a result of this:
Re-installa 2.x version of WordPress.
- Log in to your blog.
- Click Tools > Import. The “Import” page is displayed.
- Click the WordPress item near the bottom of the “Import” page.
- Click the Browse… button. An “Open” dialog is displayed. Select the file that you saved in phase 1, and click the Open button. The “Open” dialog disappears.
- Click the Upload file and import button. All the content in the backup file should be imported back into your blog.
If you followed the FTP step in phase 1, navigate to the files you downloaded, and copy everything in the plugins/ folder to the plugins/ folder in your WordPress installation. Do the same thing with your themes/ folder.