For the reports, you can delete an attribute if required. Click on Reports link available in the left sidebar. The sub-links appear as below.
Click on Attributes link. The list of all attributes appears.
Locate the target attribute.
In Action column, click on Delete button.
The backend system asks you confirm if you want to delete this attribute. Click on Ok to confirm it.
Note: When you delete an attribute, it is removed from all report types where ever it is added.