There are few ways to export content of your hubzilla channel. First of of course, you need to login to your hubzilla account at https://hub.disroot.org (dont forget to use your disroot email account for that like, email@example.com)
Going to this url: https://hub.disroot.org/uexport/basic will: Export your basic channel information to a file. This acts as a backup of your connections, permissions, profile and basic data, which can be used to import your data to a new server hub, but does not contain your content.
Going to this url: https://hub.disroot.org/uexport/complete
Export your channel information and recent content to a JSON backup that can be restored or imported to another server hub. This backs up all of your connections, permissions, profile data and several months of posts. This file may be VERY large. Please be patient - it may take several minutes for this download to begin.
You may also export your posts and conversations for a particular year or month. Adjust the date in your browser location bar to select other dates. If the export fails (possibly due to memory exhaustion on your server hub), please try again selecting a more limited date range.
To select all posts for a given year, such as this year, visit https://hub.disroot.org/uexport/2018
These content files may be imported or restored by visiting /import_items on any site containing your channel. For best results please import or restore these in date order (oldest first).