Remove uniqueness of index in PostgreSQL

Question

In my PostgreSQL database I have a unique index created this way:

CREATE UNIQUE INDEX  ON  USING btree (my_column)

Answer 1

Searched for hours for the same quesiton and doesnt seem to get a right answer---- all the given answers just failed to work.

For not null, it also took me some time to find. Apparently for some reason, the majority-certified codes just dont work when I use it.

I got the not null version code, something like this

ALTER TABLE tablename
ALTER COLUMN column_want_to_remove_constriant
DROP NOT NULL

Sadly changing 'not null' to 'unique' doesnt work.