Unless something else is explicitly informed in a particular case, you will be able to upgrade your application simply by installing the new version. It will override the existing one automatically without any special set up or user intervention.
For paid distributions, we recommend to upgrade your package through the same channel you used to get it the first time. Even though, all applications are exactly the same regardless the distribution channel, the billing process might differ. As an example, we distribute our paid applications in a "try & buy" philosophy, it means that you can download the application for free (Silver version) and use it without time constraints with restrictions in some features that will be unlocked once you get the activation code. But app stores for instance use a different approach, you may pay to download your application, so you get the Gold version from the first time and no activation code is required.