I think your upgrade failed at some step to copy all the files.
If you do not have custom files in your store, what you can do is the following:
Take following directories from abantecart cart distribution of your version and copy over your directories completely replacing them.
admin/controller
admin/language
admin/model
admin/view
storefront
code
You might need to do the same for extensions, but if you have some custom extensions, you can not replace extension folder completely