dbltoe:
Also, you might want to come up to 1.5.8a if you are relying on PayPal. There have beren a LOT of changes since 1.5.6c. Most problematic of all is that most servers/hosts are dropping PHP 7.4 and 1.5.6c is designed for PHP 7.3. Your database could start throwing errors as well. 1.5.8a works with a higher database version as well.
Not trying to throw scare tactics at you but, the longer you wait, the more difficult you may find your upgrade to be. In your case, I would recommend starting at https://docs.zen-cart.com/user/upgrading/detailed_upgrading/#0-new-version-familiarization-optional
I downloaded the 1.5.8a to server 2 times.
Each time I never saw anything like the option to upgrade database from 1.5.6c to new version and the admin area says that it needs upgrading and I can find no sql upgrade thing in any of the support documents.
The upgrade removed a lot of data like customers, products, orders etc.
I did have to upgrade php to 7.4 but I didn't go higher as I had to lower it last month or so ago as it caused another program I have on same server to quit working but I cannot remember how high the host raised the php to cause the problem.
The upgrade did say 7.4 "would work"
I basically replace the database after the first load and site worked except attributes were causing problems. But at that point not being able to upgrade the database, I downloaded again as I think I basically had a 156c database running on 158a files.
I tried to reinstall the zeninstall page but again no mention of a way to just upgrade the old database like the guides tell me or rather show pictures of.
I re-copied the original live database and the second upgrade attempt once again deleted a load of old stored data.
Also if the database is so different, will I actually lose all order and customer and product information as the upgrade did remove all that data and left a bare bone database.?