Once you install, use and like DJ-MegaMenu Free you can easily upgrade to Professional edition. See how to upgrade from free to the professional edition.
Steps to do an upgrade from Free to Pro
1. Purchase the DJ-MegaMenu subscription
2. go to My Account and find your license number
Now copy the licence key and paste it in the DJ-MegaMenu module (1)
and click Go Professional (2).
Now the license key is entered and confirmed (see below screenshot [1])
and you can upgrade to Professional Edition (2)
after that you'll have Professional Edition installed: