As root:
aptitude
Find drush under PHP.
At the bottom of the information about the drush package, there's an i that means installed next to 2.0 and a p that means no packages or config files or anything are present next to drush 3.3.
Type + when the drush 3.3 line is highlighted.
Then type g to upgrade (twice, first it takes us to a confirmation page).
Note: On Agaric's servers the package list is updated daily by a cron job, but updating the package list can be invoked by hitting u if necessary.
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