JS multiple functions don't work

JS multiple functions don't work

I would like to know how do I make the image change to another one, then
change back to normal, cuz the following code doesn't works:
function change(){
img = document.getElementById("img")
img.src = "Login_img2.jpg"
img.onclick = "change2()"}
function change2(){
img = document.getElementById("img")
img.src = "login_img3.jpg"
img.onclick = "changeN()"}
function changeN(){
img = document.getElementById("img")
img.src = "login_img1.jpg"
img.onclick = "change()"}