With your Dashboard visible, click on the cross-in-the-circle icon in the bottom left hand corner. When the little Widget draw opens, click the one called 'Widgets'. This will open a palette up, and the Widgets you're able to delete will have a little icon of a minus sign on a red circle next to them. Click this and it gives you the option to move them to the Trash, where you can delete them just as you would any other app or file.