In order to edit or add a new attribute set please go to Admin Panel > Stores > Attributes > Attribute Set.
Afterward, you choose the attribute set you want to edit or press Add Attribute Set in order to add one.
New Attribute Set
1. Insert the name of the attribute set in the Name field.
2. In the Based On field choose already existing attribute set a new one will be based on.
3. Press the Save button.
Edit Attribute Set
Once new attributes are created you will see the attribute set edit page with an Attribute Set Name that can be edited, the Groups of Attributes assigned to this attribute set and Unassigned Attributes as well.
In order to add the attribute to the already existing group you just need to drag and drop it in the chosen group.
You can add the new group by pressing the Add New button. Besides, you can delete the attribute group simply by clicking on it and pressing the Delete Selected Group button.
Once you have finished don't forget to press the Save button.