1), Download a custom model, (example named ssj4goku.mdl)
2), go to "steam/steamapps/yourusername/game/ESF/Models/players"
3), Search any folder you want to replace the model with, so lets say ssjgoku, search the folder name SSJGOKU.
4), in that folder you'll see "ssjgoku.mdl", remove that one (or make a backup) and put ssj4goku.mdl in that folder. Once you have done that, RENAME ssj4goku.mdl to ssjgoku.mdl and you're done, play ESF and you see the new replaced model..
Yup, same thing. just make sure the model you attempt to replace should be exactly the same file name of the folders and or original file name. So, example. In models/players/trunks <-- the folder name is trunks, so the model name is also named trunks.mdl. If the model name is not exact the same as it used to be. Such as you add "trunkssj4.mdl" in the trunks folder and remove trunks.mdl the game will not work.