go to where ESF is install
(default part): My Computer, C:/Sierra/Half-Life/esf/models/player
(Steam default part if you installed it though HL2) My Computer, C:/Program Files/Valve/Steam/SteamApps/[Your Steam username]/half-life/esf/models/player
Unzip or Unace the model to one of the player folders depending on what it replaces example:
If I download a Gohan model and it say replaces the current Gohan model i then go to where i have ESF installed go to the models folder then to the players folder and unzip it into the folder called "gohan" if it has say a SSJ model verison also i would unzip the SSJ verison into the folder called "ssjgohan". When it says do you want to replace the models say yes I make backups of the real models just so i dont have to reinstall again just incase it mucks up. Hope this help ya