You can delete a custom community by selecting the gear icon to the right of the custom community name.
When you select the gear, options on how to edit a community
Manage Coaches
This gives you the ability to add or remove coaches to the community.
Manage Clients
This gives you the ability to add or remove clients to the community
Update Community
This gives you the ability to rename the community. This works for the 'general' community and any custom communities.
Delete Community
This will remove the community. Once you delete it, it cannot be recovered. You can only delete custom communities.
Make Visible
This option gives the ability to hide a community that you are currently not using.