how do I set columns.column_comment?

[mysql]

How do I set information_schema.columns.column_comment?

When I try to update information_schema.columns.column_comment directly, I get this error:
#1288 - The target table COLUMNS of the UPDATE is not updatable

I know I can add the comment at table creation, but I would like to change it after table creation.

I would think I could do this through ALTER TABLE:

alter table
ctest
change column
i int(11) comment 'just some integer'

... But that doesn't seem to work. Help?

Thanks!