Besides what Bob said, you need to loosen your parking brake, here's how you do it.
First, get a large nail or screw about 3" or so long, and about 1/8" or so thick.
Now, open your drivers side door and squat by the vehicle.
Make sure the parking brake is OFF.
Look at the bracket for the parking brake and there is a small hole in the side of the metal on it (on the side facing the center console, lol).
Reach under the truck with a gloved hand and grab your parking brake cable and pull it towards you and down as hard as you can.
With your other hand put the nail or whatever straight through that hole. Release and pull on the cable until the nail goes straight in.
Carefully release the cable and the nail will hold the pawl. Then the tension will be released and you should be able to do it.
To minimize how long it takes you to adjust them, your drums should BARELY FIT on the shoes. Make sure you turn the adjuster to make this so.