1. Mark all the articles as read in the newsgroups you wish to
remove.
2. Exit Yarn.
3. expire -r news.group.one news.group.two news.group.three
4. rmgroup news.group.one
5. rmgroup news.group.two
6. rmgroup news.group.three
7. edit the newsrc in your home dir so that souper will not download
any new articles in the groups you just removed from Yarn.
Steps 1 and 3 are important. If you do not first expire the
articles in the groups to be removed, the space allocated in the
news.dat file occupied by the articles of the removed groups does
not appear to be made available for future articles. (they seem to
never expire since the group has been removed)
I maybe wrong on expire not expiring articles in groups that have
been removed with rmgroup. But it does not take much time to mark
all the articles as read in the groups to be removed, and then
expire all read articles in the groups to be removed. Better safe
than sorry.