Put delimiter. And remove ;
after END
.
DELIMITER $$
CREATE TRIGGER remiseazero
BEFORE INSERT
ON wp_stattype2_3_activite
FOR EACH ROW
BEGIN
IF (NEW.latestversion = 1) THEN
update wp_stattype2_3_activite set latestversion = 0 where typecas = NEW.typecas;
END IF;
END$$
DELIMITER ;