You cannot update directly from RRF 2.05 to RRF 3.3, you must first update to 3.0.
If you still have access to DWC. Upload these 3 zip files, one at a time in the system tab. Don't extract them. Reboot after each. Use M115 to verify the firmware has been applied.
https://github.com/Duet3D/RepRapFirmware/releases/download/2.05.1/Duet2Firmware-2.05.1.zip
https://github.com/Duet3D/RepRapFirmware/releases/download/3.0/Duet2and3Firmware-3.0.zip
https://github.com/Duet3D/RepRapFirmware/releases/download/3.3/Duet2and3Firmware-3.3.zip
That will get your firmware and DWC up to date.
If you do NOT have reliable access to DWC, you can do the manual update approach either by placing the firmware files on the SD card and using USB terminal to send the commands to update, or by using Bossa to directly flash the 3.3 firmware. Either way you'll need to manually update the DWC web interface files on the SD card manually.
Full details for firmware update options are found here:
https://duet3d.dozuki.com/Wiki/Installing_and_Updating_Firmware