For limited budgets, install a fresh version of the latest OC version on a separate development / virtual server. Then, use this extension tool to migrate the essential data: https://www.opencart.com/index.php?rout ... sion_id=17
. If further data should be migrated, then you'd have to expand the budget and to create a new service request in the Commercial Support section of the forum when ready.
The most generated errors being found on Opencart forum originates from contributed programming. The increased post counters are caused by redundancies of the same solutions that were already provided prior.
Programmer / Opencart Tester