So I did that and I was able to successfully change my resolution but sadly the text was still very blurry and the menu boxes have turned black. Now i'm wondering if this is just a video card problem?
I believe you can access the .cfg using notepad. The location is: C:\Users\*username*\Documents\ArmA - ArmA.cfg
Open it using notepad. Then navigate through the lines, you can see these two:
Just change the value to your native resolution, save and close. Try run the game once again and see if it works.