You will need to ensure you have purchased each application for your license that you intend to utilize before you upgrade. Then you will likely want to delete all the following folders and re-upload our core software again as nulled software can contain backdoors, issues, modifications, etc... that will cause errors, major security holes, or potentially loss of your license.
You will want to keep only any files that are user generated attachments or software custom settings (e.g. conf_global.php, constants.php). If you have any third party add-ons, please ensure those are not nulled either or again, you'll be causing the same issues.
You can delete the following. When in doubt, compare it with a fresh download from the Client Area.
applications (keep third party applications that are from the marketplace but remove all core/third party nulled applications)
api
datastore
oauth
plugins (keep third party applications that are from the marketplace)
system
404error.php
Credits.txt
error.php
index.php
init.php
sitemap.php