.dll file are not replacing when install new set up.

[C# Programming]

Hi to all,
I have made a set up of a project which use some dll files.When I install the setup with version say 1.0, it is installed properly.

I have another set up of same project but this updated say 2.0
Now I nstall 2.0 without uninstalling 1.0 to the same path(path of 1.0).
2.0 replace the 1.0 but those dll files are not replacing, still there are dll files of 1.0 are present.

Please guide me how to solve the problem.

Thanks in adv.