Yes, you can! All you need to do is follow the steps below:
1. Navigate to 'My campaigns', select a campaign and click on the 'Ad sets' tab. Select the Ad set and click 'Actions' at the top of the table.
2. Click on 'Edit targeting...'
3. Make your changes in the targeting pop-up and click on 'Apply changes' to send the changes to Facebook.
Please note that changes in your targeting will not affect the tracking URLs.
4. You can now see the new targeting in the Ad set view.