Syntax:
PURGE {MASTER | BINARY} LOGS TO 'log_name'
PURGE {MASTER | BINARY} LOGS BEFORE 'date'

Deletes all the binary logs listed in the log index prior to the
specified log or date. The logs also are removed from the list recorded
in the log index file, so that the given log becomes the first.

URL: http://dev.mysql.com/doc/refman/5.0/en/purge-master-logs.html

