Hi Reza,
With every new version, we also produce a tool that can analyze your code and help you identify what needs to be updated. Because you are going from 7 to 8.2, you will need to the upgrade to 8 first (using the tool if needed), and then to 8.1 and 8.2. You will find the tool will show you a lot of occurrences to change, however, most of the will be the same calls and are easy fixes.
http://devnet.kentico.com/documentation/api-changes/kentico-8-2