Main firmware versions 1.18 and earlier on the Duet WiFi used a DuetWebControl.bin file. If your main firmware is 1.18 or earlier, you need to update it before you can run more recent versions of DWC. See https://duet3d.dozuki.com/Wiki/Installing_and_Updating_Firmware#Section_Upgrading_a_Duet_2_Wifi_to_firmware_1_19_or_later_from_1_18_2_or_earlier and https://duet3d.dozuki.com/Wiki/Installing_and_Updating_Firmware#Section_Upgrading_a_Duet_2_WiFi_or_Ethernet_to_firmware_1_21_or_later_from_1_20_or_earlier. Latest stable firmware is 2.02.
If you are already running recent main firmware (2.02 is recommended) then you can just upload the zip file through the Settings General page of DWC.