I imported a database into my nation and now I have almost 6000 duplicates
You can delete people using these steps.
1. Filter for the people you want to delete.
2. Use the actions drop down menu to add them to a list.'
3. Open the list and choose Delete > Remove people from nation.
You can find full instructions here - http://nationbuilder.com/how_to_create_a_list#database
Complete and current information on how to use NationBuilder is available in the documentation section.