D-Link DSL-4320L User Manual page 22

Section 3 - Getting Started
In order to secure the router, please enter a new password. You will be
prompted for this password every time you want to use the router's web
configuration utility. Click Next to continue.
The Summary window will display your settings. Click Next if you are
satisfied, or click Back to make changes to them.
D-Link DSL-4320L User Manual 18