Capsizing on purpose in controlled conditions is a great way to familiarize yourself and your crew with what to do to recover. In 5-8 you and your crew should be able to capsize the boat - get to leeward, maybe even stand up and grab the trapeze and lean out.
If you have turned turtle, and you have a sealed mast, you should be able to get the boat back on its side for final righting. What you want to do is walk to the back of one of the hulls, depressing that corner of the boat. That should get the mast somewhat to the side, and it should then be able to rise to the surface.
Get the boat oriented with one side mostly towards the wind. Grab your righting line, and stand on the leeward hull. Walk towards the stern - pull on the line to steady yourself and add a little oomph. The stern on that corner of the boat should depress, and as a result the mast will no longer be pointing straight down. If the mast is sealed it should now be able to rise, putting the boat on its side. Be ready to move back to the center of the hull quickly as this happens - the H-16 bows and sterns have little bouyancy, and you could end up in another unhappy position. Now you should be able to right the boat as normal. Also, before all of this, make sure that your sheets are uncleated and free to run. As the boat comes back upright, move between the hulls and grab ahold of the front crossbeam as the hull comes down to the water. Your weight there can help prevent a new capsize in the other direction, and it's an easier location to reboard the boat. You can also hold on easier if the boat starts to move on it own.