Most ISP have there own modems or some that D-link has given them to use and ISP put there own FW on. I presume this is a retail modem and not from the ISP, in which yes, D-Link should have some information regarding.
Is the modem experiencing problems? If so, post about the problems. If your not experiencing any problems then we recommend not doing any FW updates.
"If it works, don't fix it!!!"
Let us know how it goes.