remove duplicates in a column

remove duplicates in a column

I have the following query to basically find all duplicates in my username
column:
SELECT `username`
FROM `instagram_user`
GROUP BY `username`
HAVING COUNT( * ) >1
How do I remove all the duplicates, such that it will only leave me with
one unique username in the table? I don't care which entity it is that is
persisted or removed, as long as there's one unique username in the table.