Creating an patch program to update a client application

I am working on a windows application .net 2.0.

I would like to be able to write my own patch application myself that would update small changes in my main application that has been installed on the customer's computer.

I would like for them just to install a small patch, rather than build a setup program.

Can anyone point me in the right direction for creating a patch application for a windows application.

Thanks very much in advance,