The grid2grid command converts a mesh with one element type to a mesh with another. The conversion type is determined by the second argument.

grid2grid / ioption / [cmo_sink] / [cmo_source]

ioption: is a character string that determines the element type of the source and sink meshes. There is no 'default' option - this argument must be specified.
quadtotri2   quad to 2 triangles, no new points.
prismtotet3   prism to 3 tets, no new points.
quattotri4   quad to 4 triangles, with one new point.
pyrtotet4   pyramid to 4 tets, with one new point.
hextotet5   hex to 5 tets, no new points.
hextotet6   hex to 6 tets, no new points.
prismtotet14   prism to 14 tets, four new points (1 + 3 faces).
prismtotet18   prism to 18 tets, six new points (1 + 5 faces).
hextotet24   hex to 24 tets, seven new points (1 + 6 faces).
tree_to_fe   quadtree or octree grid to grid with no parent-type elements.

[ cmo_snk / cmo_src ] : are the mesh_object names. cmo_src is the original grid. cmo_snk
            is the name for the new tet or triangle grid. These may be the same grid, if so desired. If both are left blank,
            the current mesh object will be used. If only one mesh name is given, it will be used at the sink mesh, and the
            current mesh object will be used as the source.

grid2grid / hextotet24  cmo_tet / cmo_hex Convert each hex element in cmo_hex to 24 tets and name the new grid cmo_tet.
grid2grid / quadtotri4 /  new_mesh No source mesh is given, so the current mesh object (which is a quad mesh) will have every quad converted into 4 triangles, and saved as new_mesh.
grid2grid / tree_to_fe / new_mesh /  octree_mesh Every element in octree_mesh will be scanned to see if it is a parent element. If it is, it will be removed, so only the leaf elements remain. The result will be stored in new_mesh.