Welcome, Kelly. I browsed the manual for that ADSL router, and while it has one knob which might be used to assign certain traffic higher priority -- ATM priority / IP Precedence, described on page 45 -- this is not useful to your purposes, which is to actively shape traffic by managing bandwidth.
There are solutions, but not through using this device.
This forum is focused on the BSD operating systems, and we would generally recommend using one of the BSDs on a computer with two or more network interfaces, acting as a router, to shape the traffic so that your ADSL bandwidth is actively and appropriately managed. In that event, the D-Link device would only be used between the computer running BSD and the Internet, and not be used for your local network in the apartment. Yes, you would need additional networking equipment, such as an Ethernet switch, along with the computer that is acting as the router.
I cannot tell, from your one and only post, if you stumbled on this forum by accident, or if you are a BSD user. But just to give you a start in thinking about possiblities, here is a link to an ADSL traffic shaping configuration example from OpenBSD's PF User's Guide, showing some traffic shaping rules that may be similar to the kinds of rules you might want or need. It is from the chapter on packet queuing and prioritization.
In case you don't know, OpenBSD is one of the BSD operating systems, and PF is its famous packet filter, used for firewall configurations when OpenBSD is used as a router, which is quite common.