You can get this version from download here: http://opensolution.org/download/
You can test this version here: http://opensolution.org/Quick.Cart/demo/
Changes in v2.1 are here: http://opensolution.org/download/Quick.Cart/changeLog.txt
HOW TO UPDATE FROM v2.0? 1. We changed database structure but You can download new version and overwrite all files in "db/" directory. We added one field in files: db/*_products_files.php, db/*_categories_files.php Database structure here: http://opensolution.org/download/Quick.Cart/other/v2.x_db.png
If You want an update from Quick.Cart v2.0. Check the changes using the Total Commander. Select a file in QC v2.0 (first column) and the same file in QC v2.1 (second column) and click in menu 'Files' > 'Compare by Content'. You will find any changes we've done.