custom os

Hello, I would like to know if it is possible to overwrite ISP OS on my modem-router combo (D-Link 6850U), I been trying to find the answer online but was not able till now. If someone know how to do it or even has experience in it I would like to hear it out.

Other than having Chrome open with one of the tabs playing Pandora, and 1 Sticky Note on my desktop there are really no other programs running (see picture for most active programs). The issue seems to happen when I do not touch anything on my computer and there is no input for about 5 minutes...