I want to remove the top part of the bottle or scale it down (that part only) because the real bottle has a small diameter opening and that's what I want and then use the cap. How can I do that?
Yu can choose it from "layers' and delete using "delete" icon on the button of panel or delete from screen with 'Delete" key.
Seletion tool have an option in his menu "Group slect" toggle button. Uncheck it from group select position.
define small? you want the top hole to be thin or less thread
1. open the model in photoshop and cut the top... that will allow you to adjust it without changing the bottom but if you want the hole to be thin then imo a remake of the full model is best