I actually want a clean magento 1.9, without any modules/extensions/themes, but would like to keep at least products and customers. Orders are good to keep, but not necessary.
Now I tried:
A fresh install. Trying to use Magento's built-in import/export customers and products, but errors were there. Something like "field value not valid" or "field value empty." Seems Magento 1.5 and 1.9 import/export not compatible?
Download Magento full package to my server and then run initial setup with the old 1.5 database, hoping that it would upgrade my database automatically. At some point there was a server 500 error. The old Magento does have some extensions/modules/custom themes.
Any advise? What would be the best way to achieve my goal? Thank you.