Upgrade osCommerce for php 5.6 / php 8

This is a 2 step project. We've been running OSCommerce 2.2 on a server running PHP 5.3 for over 15 years. We're now migrating to the new php 5.6 and then php 8, but the old OSCommerce website is giving us lot of errors. So we would like to upgrade immediatly our current OSCommerce to php 5.6 and in while we make use of this first upgrade we need move on to PHP 8. Please let us know estimated time involved, and your bid. Thanks!