Before starting, you will need to download two things. 7-Zip[www.7-zip.org] and Notepad++[notepad-plus-plus.org].

Firstly, go to your Documents folder and locate the folder "DeadIsland" in it.
Go to "out" and in there, create a folder named "Data". And inside Data, create another folder named "Skills".

After finishing with the second step, go to the game's directory located in C:\Program Files (x86)\Steam\steamapps\common\Dead Island\DI and locate the Data0.pak file.

With 7-Zip installed, click on the file with the right mouse button and open it with 7-Zip.
Inside Data0, locate "default_levels.xml" inside Data\Skills. Copy that file into that another Skills folder you created earlier.

Inside the Skills folder you created, open the default_levels file you copied using Notepad++.
Then, press CTRL+F and search for "Camera".

After that, you should probably be seeing this.
62.5 is the game's standard FOV. Erase the number and change it to whatever FOV you'd like. Let's try 90.

After changing it, save the file. Then click on it with the right mouse button, go to "Properties" and set it as "Read-Only" then apply changes.

Can't see the difference? The image below shows the game on it's standard FOV of 62.5