The next background image is not updated when I press on the button to go to the next frame I'm trying to make this tutorial : 

https://www.youtube.com/watch?v=zmZ0gVLTTB4&amp;t=180s

Go to minute 3:00,please. He loaded a list of png files and he gone until the last one. When he pressed the button to go on the latest frame,the background image on the 3D window of blender has been changed with the latest image on the list. I did the same,but in my case if I press the button to go on the next frame,I see always the first image of the list. Do you know why ? thanks.

PS : I added my blender file.
Not sure how many images are in your folder but you selected to just show 2 of them. Try bump up the number and see if it works. Your file did not have any images so could only test with my own samples but it works as advertised...