first of all, thanks a lot for your help!
So it seems this could be our solution, which would be great.
Here are pictures of our cables, maybe you can tell me, if our FG30E is terminated directly with our internet.
I am super sorry for the chaotic cable management, this wasn't my fault. :-)
This is our FG30E, below that, you can see our Ethernet Access below (OneAccess 1322).
Here you can see the yelow cable in "wan", which is connectect with the Ethernet Access.
The Ethernet Access (OneAccess 1322) got a cable, which goes straight to the phone line jack.
The white/grey cable in the FG30E Port 3 goes to the "wan" port in our router (Fritz.Box).
This is our beautiful router. Here you can see (on the left) the grey/white cable from the FG30E which goes to the "wan" port in our Router.
The two yellow ones are going into our Ethernet-Plugins from the Building.
Here are two more pictures without any comment
My question: Can I pull the port 3 cable (white/grey), which is connected from FG30E Port 3 to our Router WAN Port, without crashing the internet in our building.
Otherwise I have to do it on the weekend when nobody is here.
Thank you very much guys and I am sorry for my lack of knowledge.