From PostgreSQL wiki
ALTER AGGREGATE -- change the definition of an aggregate function
ALTER AGGREGATE name ( type [ , ... ] ) RENAME TO new_name ALTER AGGREGATE name ( type [ , ... ] ) OWNER TO new_owner ALTER AGGREGATE name ( type [ , ... ] ) SET SCHEMA new_schema
ALTER AGGREGATE changes the definition of an aggregate function.
You must own the aggregate function to use ALTER AGGREGATE. To change the schema of an aggregate function, you must also have CREATE privilege on the new schema. To alter the owner, you must also be a direct or indirect member of the new owning role, and that role must have CREATE privilege on the aggregate function's schema. (These restrictions enforce that altering the owner doesn't do anything you couldn't do by dropping and recreating the aggregate function. However, a superuser can alter ownership of any aggregate function anyway.)
- The name (optionally schema-qualified) of an existing aggregate function.
- An input data type on which the aggregate function operates. To reference a zero-argument aggregate function, write * in place of the list of input data types.
- The new name of the aggregate function.
- The new owner of the aggregate function.
- The new schema for the aggregate function.
To rename the aggregate function myavg for type integer to my_average:
ALTER AGGREGATE myavg(integer) RENAME TO my_average;
To change the owner of the aggregate function myavg for type integer to joe:
ALTER AGGREGATE myavg(integer) OWNER TO joe;
To move the aggregate function myavg for type integer into schema myschema:
ALTER AGGREGATE myavg(integer) SET SCHEMA myschema;
here is no ALTER AGGREGATE statement in the SQL standard.