If you want to upgrade Greater Shadow Amuli, then you require two vials for the coat and leggings.
If you want to upgrade armor other than amuli, then you need to apply two oils to Glyphs of Alteration and use the resulting Prismatic Glyphs on the upper and lower portions of the suit.
Note: Although the oil is Attuned and Bonded, the armor is not. If you can find someone with the oil then they can upgrade a suit for you. The same applies for the Prismatic Glyphs, except the glyphs are not attuned or bonded and can be traded freely also.