After seeing this page press the "EDIT" button located in the top left corner of your screen:
Each Item on your screen will now allow you to either delete it or move it. If you are on iPhone you can drag from the right of each item and move it up or down with respect to the other items of it's type (destinations, activities). If you are on an Android phone please use the blue arrows shown bellow:
Finally click the done button in the top right corner:
And don't forget to save your trip!!!