I configured my Fritzbox router at some point, but I've completely forgotten the login details. Now I want to change the Wi-Fi password because my roommate is moving out. Can I do that without the admin credentials or do I have to reset the router?
You won't get in without the admin credentials, sorry. You can't just go into the web interface and change the Wi-Fi password without logging in first. And no, you can't access it via Wi-Fi itself either - that's exactly what the security here is supposed to protect against.
Your only option is to reset the router. With a Fritzbox, there's a small reset button (usually on the back or bottom, sometimes hidden in a recess) that you need to press with something pointed like a paperclip for about 10-15 seconds while the device is on. After that, the router restarts and all settings are gone - including the old admin credentials. Then you can log in with the default access data (usually admin/blank or something similar, check the manual or the back of the router).
Important: After the reset, you'll also lose all your other configurations - so your internet settings from your provider, any port forwards, everything is gone. After that you'll need to set up the router from scratch. It's a bit of work, but if you don't have the access credentials anymore, you don't have any other choice. This time write down the admin credentials or save them somewhere so this doesn't happen again.
Log into answer.
