I haven't updated mine for AGES and couldn't get it to work even with the new URLs in the url.ini file, but I have found this to work:

Go to:
http://www.grisoft.com/us/us_updt6.php?lng=fe

Take note of your version number (Information tab in Control Center), choose the .bin file name you require and then download it by FTP from:

ftp://ftp.grisoft.com/pub/softw/60/fe/

Save it to the "update" folder and then load AVG - it will open a window and automatically process the update file.

Gareth