Help Flashing FritzBox 7530

Good morning,
For some time I have been a user of OpenWrt, with which I am extremely satisfied. So far I have been doing the Flashing of OpenWrt in FritzBox an acquaintance. I don't know much about informatics, only what I have been able to learn for myself. Well I'm going to the topic. The moment I want to try Flashing OpenWrt on a FritzBox 7530 by myself. I have looked at the following link,, but I still do not know how to do it and that everything goes well. I am a Mac os x user. Could someone help me with what programs I have to use and how to do it correctly?
thanks in advance and good day everyone