Here's your new modem
It has both a USB port and an ethernet jack. This is pretty common on both DSL and Cable modems. You'll use the ethernet port to connect to your DLink router, just as you do now with the DSL. Your DLink should continue doing exactly what it has been doing. It shouldn't need to change, unless it's some bizarre case of being incompatible with the cable modem.
I'm not sure of the specifics of your situation, but you may have to adjust some of the settings in the DLink so that it will be able to 'see' the Internet. The last time I had a cable modem, if I remember correctly, my router was set up in a more-or-less 'Automatic acquire' mode for the WAN connection (router's connection to the Internet). It grabbed the DNS & gateway info automatically. With my DSL modem, this had to be changed to a 'PPPOE' connection where the router supplies a Username/password to the modem for the connection to my DSL provider's (Verizon) network.
The tech guy doing the install ought to be able to help you with this setup.
The UBS ports on the back of these things are for networking without a network. For situations where a customer doesn't have a router. You can plug these modems directly into a PC/Mac with a USB cable and it'll provide an internet connection. With a router, you wouldn't be using this feature. But with some modems (my DSL modem for instance), it's also the only way to directly configure them and/or do firmware updates.
When I had a cable modem, I never had to do anything with the cable modem itself other than plug it in; AC, Cable, ethernet to router. All of the settings that mattered were done to my router's config settings.