CPAN download sites

When I first set up cpan installer, it asked me to select from a list
of ftp sites it will use to do downloads.  Now I found many of what I
selected are hard to connect -- I often need to wait for hours for the
failed connect to pass.  I wish to update the list but cannot find it
in "/root/.cpan" location.  Could someone suggest how can I update the
ftp site list?

Thanks!
Zhiliang