Repetitive registry entries of software installed by Installshield 2011 Express Edition

I have developed a utility billing software that is being used by many customers.   Every time I make a change, recompile and create a new setup.exe with Installshield 2011 Express, I update the product version and product code. I do not change the upgrade code. This causes repetitive entries in the add/remove programs, which seems to eventually cause problems with the operation of my program.  If I do not change the product code, my program has to be uninstalled before the new release can be installed.  Is there a way to make Installshield go ahead and install the new release over the older release without having to uninstall first, and not create multiple entries in the registry and add/remove program list?