This article will show you how to make a field set Inactive. This will not delete the field set, but it will make it unavailable for users.
Important Note:
You must make a field set inactive before you can delete it.
Who can use this feature?
System Administrator | Owner | Publisher | Author
Instructions
Navigate to Modules, then Content, and then Form Center:

Select the Field Sets tab:

Click Actions next to your desired field set:

Select Make Inactive:

The field set will now appear as Inactive:
