Sure can. If someone changes their plans, visit "Track RSVPs" and click on the guest you'd like to edit.
To get there from your dashboard you'll click "Guest List" and select "Track RSVPs":
Once you've found the guest you'd like to edit click their name and you'll see this box:
Still have questions? We're happy to help! Email us at email@example.com or call (408)657-9652.