Never update firmware over Wi-Fi. A dropped signal during the process can brick your device. Use an Ethernet cable to connect your PC directly to the router.
Recent updates have addressed critical issues like backup file disclosure and other security flaws. D-link Dsl-124 Firmware Update Download --BEST
D-Link products have different Hardware Revisions (e.g., H/W Ver: A1, B1, I1). Installing the wrong firmware version can damage your router. Never update firmware over Wi-Fi