ERROR: cannot change return type of existing function

Error faced
ERROR:  cannot change return type of existing function
HINT:  Use DROP FUNCTION first.


this error generally comes when you trying to recreate the function having its RETURN TYPE value changed.

CREATE OR REPLACE FUNCTION seing(str char(50)) RETURNS TABLE (a varchar, b varchar) AS
$BODY$
DECLARE
.....


ERROR:  cannot change return type of existing function
HINT:  Use DROP FUNCTION first.
********** Error **********

ERROR: cannot change return type of existing function
SQL state: 42P13
Hint: Use DROP FUNCTION first.

Solution
drop function using drop command as below


drop function seing(char(50));

This is worked fine at my end. If you face the above error in future then always drop the function
as above command and
function name should contain the datatype as define in previous function.