The update fixes some minor bugs, most notably the problem that CMSimple_XH 1.5.4 didn't work with some plugins (e.g. Calendar) in PHP versions before 5.3. For Details see the roadmap archive.

• Upgrade from 1.5 to 1.5.5 (follow the upgrade instructions)
• Upgrade from 1.5.4 to 1.5.5 
  Upload the new files in the cmsimplexh-folder over your existing 1.5.4 installation. As always we recommend making a backup of your website before upgrading.