One of my friend used to use a null version of cs-cart on his online store and I just told him to buy license keys. I just bought cs-cart license keys but I dont know how to help him transfer his stores to be use licensed cs-cart without losing his data on the old shop.
Could you give me some advices?
I do not have such experience. But try to start from the Store Import addon
Note that at the moment it is available for 4.7.2 version only. You can ask this version in CS-Cart HelpDesk system
After import is completed, just upgrade the store up to the latest version in few clicks in default upgrade center
Usually, null versions have some modified files in the core. Compare your files with the official version and replace the code. We use the kdiff3 analyzer. You may find any other analyzers that will help you to find the differences between the null version and licensed one.
Then import and upgrade won't be issues for you.
Best regards, Alt-team.