How do I replace this gun with a different model? (FE GUN KIT)

This is the current gun, but i want to change the model (Image below) I tried putting the parts of the other model into this gun’s tool and it’s handle but the new gun model didnt show up, any help?
image
Gun I want to replace it with:
image

delete the previous model and put in the new model and name it tool, if that doesnt work check the script to check if it does something with the model