TP-Link TD-8840 User Manual page 15

You will then see the Figure 3-5, you will see some information such as link rate and so on.
User name and password is "admin"; if you want to change them, please go to "Management"
"Access control" "Passwords" changing them. (Figure 3-6)
TD-8840 External ADSL2+ Router User Guide
Figure 3-4
Figure 3-5
10