I found with InstallShield 2012 but it should be the same with 2010...
you have to create a "Major" upgrade. To do that, first you have to go to "Media/Upgrades" menu.
*Select "Upgrade Windows Installer Setup" and select the option "Completely uninstall old setup..." .
*Click right on "Upgrade Windows Installer Setup" and "Add Major Upgrade Item".
*Select your this item and:
- Select "Products having another Upgrade code" and specify the upgrade code of your setup(Warning: For me the option " Products sharing my Upgrade Code" didn't work...that's why I specified manualy my upgrade code!)
- Select "any earlier version"
Now the major upgrade has been created and initialized. You just have to modify the 3 followings fields in "Installation Information/General information" each time you want to create a major upgrade:
- “Product code”
- “Package code”
- “Product version”. It’s not necessary to increase the first digit. You can increase the digit that you want
Note:
if you don't modify “Package code” and “Product version” then only a minor upgrade will be realized.
that's all.