How to get iPhone 4 passcode?

My boyfriend forgot his passcode for his iPhone and I want to download instagram but it won't let me without a passcode. Is there any way to get the password or do you have to restore it. Any help would be muchly appreciated!

You're gonna have to restore it most likely

You have to go to Settings > General > Passcode and make a 4 digit passcode

Try asking your boyfriend to remember the last 2 digits or any 2 digits then list down the digits on a piece of paper what numbers he have tried. And also ask him if the numbers in the end is an even or odd. If its odd, probably it ends with 1, 3, 5, 7, 9 if its even then 2, 4, 6, 8, 0. And ask him what is it related about?

You want Instagram on your boyfriends iPhone? Since the passcode is forgotten your boyfriend probably can't even use his phone to call or text and all you are worried about is Instagram? Odd story