How do you change the way the doors unlock on the driver and passenger doors?

How do you change the way the doors unlock on the driver and passenger doors? Right now I have to press the unlock button to get out of the truck. It is almost like the doors are child locked, but if I press the unlock button I can then get out. I would like it to lock when I put in gear and unlock when I take it out of gear. I was wondering if I needed to take it to the dealer ship or if I could do it myself.