If you have one of the ARDS with the 1.54 preinstalled, there is absolutely no way to upgrade to 1.7X. Though, I sent a support ticket and got the following response (the download link is attached to the post via the Attached link field):
v1.60 and v1.71 firmware are NOT compatible with v1.52/v1.54 hardware.
v1.60 firmware was never available for download and was preloaded on newer Action Replay DS hardware, however a new v1.55 firmware is available.
The v1.55 firmware update which, is downloadable HERE, is designed for use with ONLY the Action Replay DS with v1.52 & v1.54 firmware. THIS IS NOT for use with newer hardware with v1.60 firmware preloaded.
The v1.55 firmware update includes support for a number of games including Pokemon Black, Pokemon White and Professor Layton and the Lost Future.
To update your Action Replay Media Edition:
Download the v1.55 firmware update and uncompress the downloaded file
Using the included PC software disc, install the Action Replay DS Code Manager PC software
Open the Action Replay DS Code Manager PC software
Power your console on with the Action Replay DS inserted.
From the home screen of the Action Replay, set the Action Replay DS to the update mode by selecting the update (computer mouse) icon from your consoles touch screen.
Connect the Action Replay DS to your computer using the USB cable.
When installed by Windows the Action Replay DS will be detected by the Code Manager PC software which is confirmed by the message ‘Waiting for DS’ no longer being displayed beneath the section ‘Nintendo DS’.
Drag and drop the uncompressed v1.55 firmware update onto the bar located at the top of the Action Replay DS Code Manager PC software
The firmware update will now automatically begin, the first part of the update may take a number of minutes to complete.
Select ‘Yes’ to confirm that you would like to write the new firmware, select ‘No’ to cancel at this stage.
Once the writing of the firmware is complete, the Action Replay DS will automatically disconnect from your computer.
When the message ‘Reboot your NDS now!’ is reported on your consoles screen, restart your console to complete the firmware update.
NOTE: This is a discontinued product. It is no longer sold in US retail stores & compatibility updates may not be available in the future. It's recommended that you update to the DSi Action Replay hardware to ensure future compatibility.
The DSi Action Replay is compatible with the Nintendo DS, DS Lite, DSi, and DSi XL consoles.
http://datelcustomerservice.com/files/NDS-ARDS_firm_1_55.zip