peku
2016-08-22 17:39:30
If you do upgrade in Remote Upgrade Tool 5.x.x:
You removed these folder/files
catalog/model/total
catalog/model/payment
catalog/model/shipping
catalog/model/feed
catalog/controller/module
catalog/controller/payment
admin/controller/module
admin/controller/payment
admin/controller/shipping
vqmod/vqcache/all files
vqmod/xml/expired xml-files
system/storage/modification all files (if do upgrade from Oc 2.1|2.2)

Option: before upload you can rename folders catalog to catalog-2, system to system-2, admin/controller to controller-2 etc. and then upload Opencart 2.3 files.
peku
2017-05-23 23:03:36
IMPORTANT
In your store must not be hidden files, eg. file .D_Store in folders 'payment', 'shipping', 'total', 'feed', 'module', 'farud', 'dashboard','analytics' and 'captcha'. When upgrade do to version 2.3.0.2, these folders deleted. Php is not found hidden file (it is not can remove file .D_Store) and folder removal can not be done, it do issue.