Convert Unity 3.4 build to 3.5

I want to convert my game build from unity 3.4 to 3.5. Is there something i need to check before to do that?
It’s a big game so i cann’t just convert and check whether everything is all right or not.
Thanks in advance.

Normaly there is no problem updating unity but to be sure just make a copy of the project file

Unity will show any errors/warnings that occur during the update process for the project, but other than that you will have to go through and check everything; there’s no way around this. You don’t know for sure what behavior might have been changed with the upgrade unless you test everything. For this reason it’s generally not done to upgrade the engine for a large project that’s reasonably far along, unless there’s something critical about the older version of the engine that can’t be worked around and prevents the project from being completed.