I think you need to have Access installed on your system. I just navigated to the appropriate directory, and found the latest program:
Once you open (double-click on) the program, you should be presented with the various tables in the program:
When you double-click on the Dealers Table, you should have a large list, as shown:
Then, you can delete one or all of the dealers. Be very careful of the other tables, though.
My recommendation is to always make a backup copy of the entire MDB before starting, so that you can always recover to the original. Good luck!
Note: This will only modify the available list of dealers. It will NOT modify if any individual stamp is assigned to any one dealer. If that is your goal, then you need open the "MyCollection" table and to change all of the DealerId to "0". That is a little more cumbersome, so be careful there.