Depends on the radio. I've firmware updated my TK-2180, 3180, 7180HK and 8180H so I''ll use that as an example.
You must make sure your radio is set for firmware programming. In the software, click on EDIT then OPTIONAL FEATURES. Under the tab COMMON PAGE 2, make sure Firmware Programming is checked. If not, check it and write to the radio.
To get the radio in firmware programming mode, press and hold S while turning the unit on. The display should read PROG and a set of numbers. On the computer, run Fpro.exe found in the KPG89D folder your software installed to. Make sure the Baud Rate number matches the number shown on the radios display.
Locate the firmware file (should be a HEX file) you saved to your computer and click on WRITE. Let the program run it's course (should only take a minute or two) and when finished the radio should show the checksum number. It should match the checksum number shown in the Fpro program.
I've firmware updated all my 180 series radios for MDC-1200 capability.