If you ever decide you want to change the assignment after students have begun work on it, it's easy!

From your "My Activities" home page, click the activity title, then click the assignment. That will take you to the Assignment Detail page (where you see all the student submissions).

Click the "3-dot" menu above the assignment details on the left, then click "Edit Assignment."

You'll be presented with the list of Assignment options that you can change.

Edit any of these, then click "Save." Any student beginning opening the assignment after you save the change will be operating under your new settings.