Bug fixes to v6.0 here: http://opensolution.org/download/Quick.Cart/bugfixes/bugFixes.html
Bug fixes to v5.0, v5.1 and v5.2 here: http://opensolution.org/download/Quick.Cart/bugfixes/bugFixes_v5.x.html
Documentation is here: http://opensolution.org/Quick.Cart/docs/
Upgrading from v6.0 or v5.x: 1. Upgrading database: - Copy all files overwriting the existing ones (except for the subdirectories and the "_fields.php" file) from the database/ directory in the older version to the same directory in the latest version - Copy all files and subdirectories from the files/ directory in the older version to the same directory in the newest version - Enter the settings page in the administration panel and set options, attach pages to specific functions, set login and password. Some of the settings options (like menu types, thumbnail sizes) are possible to set only by editing the database/config/general.php file. Documentation will come in handy (http://opensolution.org/Quick.Cart/docs/?id=en-requirements#5)
2. Upgrading design: This process can be time consuming. There is no automatic script for design upgrading. Before proceeding to modify the design, we recommend to create a new directory for example templates/new/ and copy there content of templates/default/, and then in administration in the settings select a skin to the "new".
Upgrading from v4.0, v4.1 or v4.2: You need to upgrade first to v5.0 and after to v6.1. Read more about upgrade here: http://opensolution.org/Quick.Cart/forum/?p=readTopic&nr=7739