Once you have created your advert you are not able to go back to step 1 to edit the features for your advert. However you can edit the features on a section by section basis to achieve the same result.
To edit the features for a section click on the "Change Features" button, this will bring up the feature selector with the current features for that section preselected.
From here you can add/remove features and the content will automatically update. Click the "Update Tags" button when you are finished editing features.