Syntax:
RESET SLAVE

RESET SLAVE makes the slave forget its replication position in the
master's binary logs. This statement is meant to be used for a clean
start: It deletes the master.info and relay-log.info files, all the
relay logs, and starts a new relay log.

Note: All relay logs are deleted, even if they have not been completely
executed by the slave SQL thread. (This is a condition likely to exist
on a replication slave if you have issued a STOP SLAVE statement or if
the slave is highly loaded.)

Connection information stored in the master.info file is immediately
reset using any values specified in the corresponding startup options.
This information includes values such as master host, master port,
master user, and master password. If the slave SQL thread was in the
middle of replicating temporary tables when it was stopped, and RESET
SLAVE is issued, these replicated temporary tables are deleted on the
slave.

URL: http://dev.mysql.com/doc/refman/5.0/en/reset-slave.html

