@hombie , You can set the modem to bridge mode and then connect your Fritzbox or another router. Both your modems are already set to IPv4. So you can set your modem to modem/bridge mode in the menu.
@hombie , We do not have a PDF.
But you can try following these instructions:
1. log on to the modem with the IP 192.168.0.1
2. enter your password
3. go to the menu "Bridge Mode
4. select "Activate Bridge Mode
5. click on "Apply changes".
Your modem will now restart. Plug a LAN cable into port 1 of your UPC Connect Box. Plug the other end into the WAN port of your router. Now your router has Internet. If you want to make changes to the UPC modem, you can log in via IP 192.168.100.1.