Cannot change name or password due to Access denied

I have an Arris Wifi Router Modem combo, Model Number DG3450. My 2.5Ghz and 5Ghz wifi connections have the same Name and Password all of a sudden and I need them to be different so I can connect to different devices. When I try to change the name and Password of the 2.5 and 5 ghz Wifi network it gives me an access denied yet I am logged into my router, it just gives me the access denied when i try editing the name or password of ether? How would I fix this, anything helps?