How can I change the texture of monster?

[Romulator]

Open the material editor and edit the material of the texture in your custom .mat file. Then open the Model Editor, and apply the new .mat file.

Then in the level editor, place a servant_grunt entity down, then click on it. There is a small directory input in the right pane. Simply change the file to the one in your custom_story/story/entity/servant_grunt folder.

If it fails to apply, delete the .dae file in your custom_story entities folder