Lock out PostgreSQL users for maintenance

Hello,

In PostgreSQL 8.4.9 with pgbouncer 1.3.4 in
pool_mode = session (but some users connect to the
database directly) - when I login as "super user" with

   psql -U postgres -W postgres

What is the command please to disconnect all
"normal users" and prevent them from connecting
again while I perform maintenance (I'd like to
rename some table columns for more consistent naming
and correspondingly change some stored procedures).

I can't find it in the III. Server Administration doc at
http://www.postgresql.org/docs/8.4/static/admin.html

Or should I edit pg_hba.conf and restart the process?

Thank you
Alex