Hi, on the
Ateca you remove screws underneath then the rest is clipped, start at one side of the exhaust and gently pull the clips out.
I found the clips running along the top edge of the diffuser difficult to remove which resulted in the small split on mine.
Fitting is easy, locate the tabs on the top edge and fit screws in the same place you removed from the original, on the
ateca you have to drill 2 holes each side by the exhausts and fit the screws provided.
Hope this helps.