You need to flip all of the Normals that are currently facing the wrong way. You can do this a few ways.
Select all of the Normals that are facing the wrong way than either press "W" on your keyboard and search the menu for "Flip Normals" or search in the menu on the left for "Flip Direction" . Also make sure your in Face select mode.
Alternatively you could select all faces or a large group of faces and press "Ctrl + N" or search the menu on the left for "Recalculate". However, this method could mess up normals that where facing the correct direction.
Select all of the Normals that are facing the wrong way than either press "W" on your keyboard and search the menu for "Flip Normals" or search in the menu on the left for "Flip Direction" . Also make sure your in Face select mode.
Alternatively you could select all faces or a large group of faces and press "Ctrl + N" or search the menu on the left for "Recalculate". However, this method could mess up normals that where facing the correct direction.