You can Delete any Sphere you have Created.

Click Your Name in the top right corner.
A menu will open.
Click on the Account Settings item.

In the My People menu.
Click on Upload Sphere Contacts item.

Click on the Menu Icon to the right of the Sphere you want to Delete.
A menu will open.
Click on the Delete item.
A window will open.
Click on the DELETE button near the bottom right corner. 

IMPORTANT: When you Create a Sphere. A Tag is Automatically Created using the Sphere's Name. When you Delete a Sphere. The Tag is not Deleted. You will need to Delete the Tag separately.
Click Here for more Information on how to Delete a Tag.

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