Router's insecure password

Hi,
Avast keeps telling me my D-Link router password is too weak and so I’m trying to change it. I’ve reached the attached screen but don’t know if it’s the right one (I’ve deleted the modem details) and am wary of going further in case I mess something up. Can anyone take me step by step from this screen to safely changing my password? I’m running on El Capitan if that’s important.

The best Place to get help With a D-Link router is at D-Link support / forum

You can’t make changes till you’ve signed in.
Unless you’ve already changed the sign in information, that would be the default sign in information.
More help with the default information here.
https://deconf.com/default-username-and-password-for-d-link-routers/