This release fixes bugs in 3.3RC2. The change list is at https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x-Beta-&-RC.
Users running Duet with attached single board computer should upgrade using the unstable feed from the package server as usual. Users running in standalone mode can use the files here.
The DuetWiFiServer.bin file remains at version 1.26 so there is no need to install it of you are already running this version.