If you still have access to DWC. Upload these 3 zip files, one at a time in the system tab. Don't extract them first. Reboot after each. Use M115 in the gcode console 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.
From there you can update to the betas manually.
You can see the change logs here:
https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x
For your config, might be a good idea to run through the configurator tool and generate a fresh set for RRF3.
https://configtool.reprapfirmware.org/Start
Backup your existing config files in the sys folder in case you want to switch back to RRF2. It’s easy to switch back and forth, just upload the zip file for the version you want and then upload your config files.
These documents will come in handy during the conversion.
https://duet3d.dozuki.com/Wiki/RepRapFirmware_3_overview
https://duet3d.dozuki.com/Wiki/Gcode