The Master Lock model 1500iD differs from other padlocks in two ways. First, instead of using the normal numerical wheel face, the 1500iD uses a button that can be shifted in only four directions. Second, the lock can be reset to any combination of button presses that you desire. Of course, you will need to know the original combination before you can reset it.
Pull the shackle toward the body of the lock until it clicks. Repeat.
Enter the old combination, and pull the shackle up to open the lock.
Push the gray reset lever on the back of the lock towards the "R" with a pen or pencil to put the lock in reset mode.
Squeeze the shackle toward the lock again twice.
Pull the shackle up. The lock should open again.
Enter the new combination. It can be as long as you like.
Slide the reset lever back to its original position.
Close the shackle. Press down on the shackle twice again, then try the new combination. It should open the lock.