You can easily export your user stories. Follow these steps

1. Go to Agile
   
2. On left menu select User Stories under "Search & Filters"
3. By default it loads all user stories.
4. To export these stories click on "CSV" icon which is visible under "Filter" Button.
   
5. Filter results based on some specific criteria and then click on CSV will only export those filtered user stories. Example is shown here