change password for DG240 router

hello….I have never changed my password for my 3.5 yr old DG2470 router and i can’t access the change password via the IP address info many people talk about online. I have tried all 6 username and password suggestions listed….advice...trying to secure the router more as it seems to have more traffic than I actually am using it for and neighbors live 100ft away...= an AirBnB trailer is right next to my shop