Project Installer or setup will install your program on any system. For updating your software, you will need to update/add the required files (.dll, .exe and other project files) on the client system.
Updating the project installer doesn't make sense because every time you make an update, you will need to install the updated installer again on the client system.
Microsoft has
Click Once technology through which you can deploy and update your application easily. It is build upon
Updater Application Block which is a part of Microsoft Patterns and Practices and gives self updating capabilities to your windows application. Below I am providing useful links which will help you understand and create a deployment and update solution for your project:
Deploying Applications and Components[
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ClickOnce Security and Deployment[
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There are other solution developed by many developers for this. If you Google for "application self update" (and similar searches), you will get many options to do it.
Hope it gives you and idea and takes you to a correct direction!
Good luck!
Ankur
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