your going to want to change the material type to either translucent or masked. to do this go into your material and select the big node that is on the right it will have the material name as the node name if remember right. now with that selected got to the panel in bottom left and one of the options there will say opaque (i think its blend mode). just change that to translucent or masked. now take the alpha channel of your texture and plug that into either the opacity pin if using translucent or the opacity mask if using a masked material.