Never update router firmware over Wi-Fi. If the wireless connection drops mid-update, the router will break. Connect your PC directly to one of the LAN ports using an Ethernet cable.
To update the firmware on your D-Link DSL2750U V2 router: dlink dsl2750u v2 latest firmware update link
To find the exact file, navigate to the or Support section of these sites, search for "DSL-2750U", select your exact hardware version, and download the latest .bin or .img firmware file (usually packed inside a .zip archive). Why You Should Update Your DSL-2750U V2 Firmware Never update router firmware over Wi-Fi
Click (or Firmware Upgrade ) on the left-side menu. To update the firmware on your D-Link DSL2750U
This means you are trying to upload the raw .zip file instead of extracting the .bin file first, or you have accidentally downloaded firmware meant for a different hardware version (like V1 instead of V2). Double-check the bottom sticker of your unit.