Just saw your email too. Are you aware that Microthemer is a plugin, not a theme? And so it needs to be uploaded via Plugins > Add New > Upload.
If that’s not the issue, there is an alternative way of installing Microthemer. Go to Plugins > Add New. Instead of choosing upload, search for Microthemer in the plugin search box. Then install Microthemer Lite. As you have purchased Microthemer, you will be able to unlock the program using your email address.
I hope that helps, Please let me know if you need further assistance.