Guild Wars 2

I am unable to transmute my Trickster’s light armour with the stats of new armour that I want. Why is this? The item does not say that it’s not able to be transmuted and I think since it doesn’t note this that it would be pretty unfair for me to have to buy it again.

Please help.

It should not have any problem with being transmuted.
However, the Trickster item you purchased is just a skin that can be applied to an item, no transmutation necessary. Just double click the Trickster Skin Piece you want and then drag the corresponding armor piece into the window to replace only the skin of your current item.

Or are you saying that you already applied the skin to an armor item and you now want to transmute the skin onto a completely different armor item to update the stats while keeping the Trickster skin?