It is not possible to delete or edit another member's comment.
Even if you are the creator or administrator of the project, the only person who can delete or modify a comment is its creator.
So you have several options:
- From the task, send a Buzz to the comment author to ask them to edit or delete the comment.
- Duplicate the task. Comments are not kept when copying. You can then add the comments you want (by copying and pasting certain comment elements from the original task for example). Verify that the other information is present, and then delete the original task.