It looks like a 15mm bolt head on mine. 1/2" drive breaker bar with a shallow socket should work just fine, I don't ever struggle, and I'm just a little guy. They also make special tools for $30-40 to aid in belt replacement. Once you get the tool on, push to the passenger side, pulling the pulley upward, releasing the tension on the belt. Hold the pulley in position and guide the belt off any accessible pulley, and slowly release the tensioner pulley back. It will move further back than you started with it, so be prepared for some extra travel as you release tension, and don't just let go unless you want to cuss up a storm and scare the neighborhood children...
If you end up loosening the tensioner's bolt, just tighten it back up something fierce and try again. Double check belt routing before starting motor, make sure the belt is riding on the pulley's correctly and what not, not riding one edge more than the other. When all is said and done, put a little push on the tensioner to "overset" the spring inside there. Kind of when you go to straighten out metal, you have to kind of over bend a little. That's just a little habit I got used to. Other than that, your good to go.
2005 Quad-Cab, Brilliant Black Crystal Clear Coat, Incubus Poltergeist Rims, Factory Powertrain and Chassis.
Driver possesses weighted right foot and superb ability to get out of speeding tickets.