Installing the mod

Hi there, I followed the install instructions (download ieb...rar, copy it in the Attila\...\data folder, unpack it there), but I must have gotten something wrong. When I tried to activate it in the Steam Mod Manager I only had the choice to upload it...? :hmm: SO where's the mistake? I didn't overwrite anything as told, because I was not sure what is meant by the "existing version". Data.pack is about 10x larger, so I figured I'd delete basically the game and kept my fingers off this one...

Could you tell me the file name, please? Thanks a lot!