SET PASSWORD FOR 'tom'@'localhost' = PASSWORD('foobar');
OR
UPDATE mysql.user SET Password=PASSWORD('new-password-here') WHERE USER='user-name-here' AND Host='host-name-here';
SET PASSWORD FOR 'tom'@'localhost' = PASSWORD('foobar');
OR
UPDATE mysql.user SET Password=PASSWORD('new-password-here') WHERE USER='user-name-here' AND Host='host-name-here';