From the Catsy dashboard, click on More and then Attributes
Open the Attribute you want to remove from an Attribute Group
For example: Brand
Scroll down to “Attribute Groups & Validation” where you can see the Attribute Group/s that this attribute belongs to.
If any edits need to be made to the Attribute Group/s you can click the “Select Groups” button
Tick and un-tick until the selection is as per your liking and click "Add"