In the next few days I have to replace the injector. I watched some videos and it looks like a very straight forward job. However, is there any advance preparation? Disconnecting the battery or something?

 

Funny, I have the same job at hand (thread here). What I read in the Haynes manual for this car (likely similar for all cars) is to disconnect the negative battery connection ( 10mm socket).
I've also read that in some cases, the car needs an update (or the ECU needs to be informed about the changed injector or the injector needs to be updated, all rather vague). If that is the case, I'd guess you need a mechanic with a capable ODBII tool...