You can mange your discussion settings as well as student discussion settings.
You can allow students to create a new discussion, edit and delete their own posts, and attach files to a discussion by changing the settings from the Discussions page.
1. In Course Navigation, click the Discussions link.
Discussion Index Link [View Image]
2. Click the Settings icon.
Discussion Settings [View Image]
3. Check the box beside the settings you would like to enable.
Student Discussion Setting Options [View Image]
You can allow students to edit and delete their own discussion posts  by changing the settings from the Discussions page.
This setting can also be changed from the Course Settings page.
Note: When enabled, this setting also applies to group discussions.
Students can attach files to discussion replies in course discussions . This setting is enabled by default and can be managed from the Discussions page or from the Course Settings page. Any attachments added to an ungraded discussion by a student are copied to the student's user files and count against the user quota. However, attachments added to a graded discussion are not counted against the quota.
Disabling this option will restrict students from attaching files in discussion topics, discussion replies, and discussions within course groups. This option does not affect your students' ability to add a file using the Rich Content Editor.
Note: If a student creates a discussion with an attached file, the file will be added to course files in the unfiled folder.