From 1.90 onwards, updating MixRack firmware from the browser is disabled by default.

To re-enable this feature you must set switch JP3 into the on position. 

This is done by accessing a set of 4 DIP switches, inside the I/O port on the C Class, or inside Power 2 on the S Class (see photos).

It is important that only switch 3 is put into the ON position.

To enable the browser updater, first switch the MixRack off, then access the DIP switches as shown in the photo below for your MixRack type.

Switch 1 – keep OFF
Switch 2 – keep OFF
Switch 3 – Switch ON
Switch 4 – keep OFF

Once the switch is in the ON position, power up the MixRack. 

Connect a computer to one of the Network ports on the MixRack and follow the Surfaceless update instructions listed here

https://www.allen-heath.com/media/dLive-firmware-update-instructions-Issue-5.pdf