I try to change the GUI icons but I succeed only for part of them. Ex: I change the icons for the inventory, but when I run the game appear the old ones ! If I delete the old ones from the sprites, some strange icons appear instead of the expected ones !
For the status bar and the other gui everithing was OK
By default, the INVENTORY GUI you see in the GUIs pane is not used in the game. It looks identical to the built-in one, but it's just a template. You need to change the script to use this GUI instead of the built-in one.
I don't have AGS with me right now, but I think there's a show_inventory function somewhere in the global script that you need to modify.