Brinks made a padlock in the past with the model number 7551, but it doesn't anymore -- all the model numbers for Brinks padlocks are now eight digits long, separated by a hyphen. If you have a resettable Brinks padlock, though, the model number isn't of great importance, because the procedure for resetting all of them is the same, whether a particular model has three dials or four. This procedure is similar to the one for resetting combinations on padlocks from some other manufacturers.
Open the lock using the current combination. Set the dials to align the numbers in the combination with the line on the front of the lock.
Pull the shackle up and swing it 180 degrees, and then depress it and hold it down.
Rotate the dials until the new combination aligns with the arrow.
Release the shackle and rotate it 180 degrees back to its original position.
Push in the shackle and rotate the dials randomly to lock the lock. It will open again when you rotate the dials to align the new combination with the line on the front of the lock.