How to Find Any Data of the Website and Edit It?

I wonder how to edit data that's coming to our computer I tryed to do it modifying the headers but's really dificult to find your goal trough the encryption and even the decrypted data should be encrypted again with the private password before being modified. I read something about edit it on a proxy tunnel wich is a connection between the computer and the router and using mitmf, I have installed httptunnel on my Kali Linux and my Windows 7 and I can't make it work, I also try mitmf and don't let me load any webpage intead of it a messege saying "waiting for proxy tunnel" shows up I though because they have to be working together. Sorry if it sound desessperated I'm absolutely new on this so any andvice is welcome.

PS: Even having httptunnel instaled I don't know how to take the adventage of this as they say "today for me tomorrow for you"