Firstly, you can delete a community only and only if your the owner of that community. If you’re a community owner and you would like to delete your community, then please follow these steps:
1> Click Communities at the top of any page, which you’ll find when you are logged in.
2> You can also get to the Communities page by clicking on ‘my communities‘ section box.
3> On the owned tab, click the name of the community you’d like to delete.
4> Click edit profile below the community image.
5> Here you select delete community.
6> Click delete on the confirmation screen.
And you are done !
Related reading: How to delete your orkut account completely !