HOW TO UPDATE / UPGRADE A THEME OR PLUGIN IN WP MANUALLY?
First thing you can not upgrade / update throughout the regular upload file in wordpress, you have to delete the plugin or theme (not child) and then upload a new one.
When you trying to update plugin or theme from a .Zip file you will get error.
This plugin is very simple tool that fix the update error. Without the need of deleting files just install like you install new plugin or theme.
Another great tool that you can use in your websites is called ‘wp rollback’, with this simple tool you can rollback to other versions of plugin or theme that you installed before from wordpress repo, in case of install issues.