I have the same problem; however, heading to that website and entering my Serial # gives the following message "The serial number you’ve provided appears to be invalid. Please try again." and doesn't allow to download the file.
I bought my gsm and sim-unlocked Hero in New York, although I live in Europe. Here is the information my phone gives me in About tab:
Firmware: 1.5
Baseband version: 63.18.55.06EU_6.35.06.18
Kernel version: 2.6.27-8dd6deee
htc-kernel@and18-2 )
Build Number: 2.73.421.5 146733 CL#61267 release-keys
Software version: 1.0.0.A6288
I would really appreciate if anyone could help me update my phone!!!