Thanks to Omeka’s API capabilities, exporting from Omeka.net to a self-hosted Omeka Classic installation is a straightforward process. Use the Omeka API Import plugin to import the data from your Omeka.net site to your new Omeka installation by following the instructions for the API Import plugin. You will want to use the section titled “With an API Key.”
Setting your Omeka.net site up to work with the API Import plugin is simple. Make sure the API is enabled on your Settings page, and create an API Key for a Super user on the site. This will ensure that all of your data, even private records, will be imported into the new site. The url for your site’s API endpoint is http://yoursite.omeka.net/api.
Additionally, you can export most of your metadata to a CSV file using this python script. Follow the link for more details and instructions.
For more information on the API settings see Manage API Settings.