Main theme package includes archive file of the plugin named STM Import Makes & Models. This plugin allows you easily import Make and Model categories in your site. This plugin automatically sets up categories relationship. It only needs to upload CSV import file (with your own categories) and set up a few options. Here you can download the latest version of this plugin.
After installing this addon plugin, you need to go Tools -> Import Makes & Models and upload your own import file.
Please check and be sure that you are setting correct Column Name from your import file.
Example CSV file is located in the plugin folder - CSV_sample.csv or you can download it here.