Version 2.2 is available for download at:
http://wordpress.org/download/
Upgrading_WordPress details the upgrade process.
Version 2.2, and previous versions of WordPress, are also available at:
http://wordpress.org/download/release-archive/
Other information:
List of files revised for Version 2.2
Visual Editor not working in 2.2
Dashboard showing access denied--error 403 (not showing feeds)
Plugin to restore Post Preview frame
How to turn-off Widgets in 2.2
