ActiveX designers follow the Automation model for upgrades. To release a new version, you supply a new type library with a new version number. To change the version number, use the SetVersion method in the ICreateTypeLib interface. This method takes two parameters, a major version number and a minor version number.
A new version that is compatible with previous versions requires only a new type library with an increment in the minor version number.
A new version that is incompatible with previous versions requires that you increment the programmatic identifier (PROGID) and supply a new type library with an increment in the major version number. You also have to update the registry to include the new PROGID and version number.
See the Automation Programmer's Reference for more information.