Hello, I cant seem to update the software on Itunes for my new Iphone 5s, any ideas?

What are you trying to update, the version of iOS that you have on your phone (7.0.4 is the current version), the version of iTunes that you have installed on your computer, or your logged in account on your computer's iTunes ? If your account then you can log out of the currently logged in account via the Store > Sign Out menu option and you will then get a Store > Sign In option. If you are trying to update details on your account then you can change some things on it via the Store > View Account menu option