Before updating, verify your hardware revision (e.g., H/W Ver: C5) on the sticker underneath your router, as firmware must match the hardware version exactly to avoid "bricking" the device. How to Install Firmware ME_1.03: Wireless N300 ADSL2+ Wi-Fi Router DSL-2740U - D-Link
To confirm details or attempt an update, refer to the following official repositories: dsl-2740u firmware version me-1.03