Bug fixes to v4.1 here: http://opensolution.org/download/Quick.Cms/bugFixes.html
Skins and plugins to v4.2 Most plugins works correctly with new version.
HOW TO UPDATE DATABASE FROM v4.0 or v4.1? 1. We DIDN'T changed database structure in v4.2. You can download new version and overwrite all files in "database/" directory (without subdirectories) from v4.0 or v4.1
Check changes using Total Commander. Select file in Quick.Cms v4.1 (first column) and the same file in Quick.Cms v4.2 (second column) and click in menu "Files" > "Compare by Content". You will find changes made by us.