Though not impregnable, locking cases like the Presto briefcase add a level of security to the carrying of important documents. If there is any chance that others have seen you input your code, changing the lock on your briefcase may be prudent. Depending on the sensitivity of the information carried in your case, periodically changing your combination may be a good idea regardless. Though more time consuming, combinations can be changed even if you have forgotten your code.
Open your Presto briefcase with the current lock combination. If you do not have the current combination, cycle through the thousand different combination possibilities until you happen upon the correct one. Overstock.com estimates this process will take up to 90 minutes to complete. New briefcases typically have default combinations like 1, 1, 1 or 0, 0, 0. Try these basic combination before setting out to cycle through all possible permutations.
Open the briefcase and locate the combination reset switch on the inside. There is some variations, but reset switches are usually located on the back of the clocking mechanism.
Determine the new lock code you wish to use. Combinations that will be easy for you to remember are advisable, but avoid numbers that others may be able to predict like your area code or simple codes like 1, 2, 3 or 9, 9, 9.
Press and hold the reset mechanism. Then rotate the lock combination to your new code and release the button.
Test the new code by shutting the briefcase, scrambling the numbers, entering the new code and opening the case. If the case does not open, you may have neglected to hold the reset button firmly enough; you will need to repeat the reset process.