Hi, Firmware update for FF linking device is described in the manual 3BDD011677-600*. You should be able to do that trough integrated WEB Server interface. Have a look also in the manual 3BDD012902-600 for FF as a paart of 800xA.
LD800 and LD 810 firmware can be downloaded by using integrated WEB Server interface. From 800xA 6.1 onwards webpage is locked from first download of LD. So webpage need to be enabled first from FF Builder (Open Project in FF Builder, go to onlien mode and enable web server from LD800/ 810 context menu) Open webpage in admin mode and browse the firmware file and load. It may require LD power cycle.