Recreating a new setup file

Question

I have written a program in windows C# 2005 and deploy the program on our production server. my manager however asked me to put more feature on the program and i rewrote everything.

my question here is do i have to create a new setup file and do a fresh new installation by uninstalling the old one from the production server? if that is the case everytime i made a little modification i have to create a new setup file and uninstall the old one and install a new one. I heard .NET resolve this issue but i am not exactly sure how it is. please advise