The link is correct but lame.buanzo.com is experiencing problems at present. You can download this instead:
http://www.gaclrecords.org.uk/FFmpeg_20 ... indows.exe
However the FFmpeg binary which that installs does not support AMR because AMR support is legally undistributable. To get AMR support you would have to compile FFmpeg from the source code:
http://ffmpeg.mplayerhq.hu/download.html
using the Cygwin development environment (the easier Visual Studio environment available from Microsoft won't compile FFmpeg):
http://www.cygwin.com/
More realistically, I would suggest you download SUPER which will convert the AMR file to PCM WAV then Audacity can import it:
http://www.erightsoft.com/SUPER.html#Dnload
Drag the AMR file into SUPER then:
1) in the output container list top left choose "WAV (audio only)"
2) in the output audio codec list top right "WAV pcm 16 little endian"
3) In the "audio" panel select 44 100 in "Sample Freq" and "1 channel"
4) Right-click > Specify the Output Folder Destination and choose a location
for the exported WAV that you can remember. Click "Save Changes".
5) Ensure the check box by the name of the file you dragged in is checked
then click "Encode (Active Files)". When a file size appears to right of the
file name under "Output Status", you're done.
If you need the file to remain in AMR format after editing, export from Audacity as WAV (Microsoft) signed 16 bit PCM, drag the WAV into SUPER, then choose AMR in the output container list at the top. Note re-encoding as AMR will reduce the quality.
Gale