Polygons > Refine subdivides polygons on the entire polygon object, or in a selected region.
4X Subdivision radio button - divide every triangle (or every selected triangle) into four triangles. 4X Subdivision causes every adjoining triangle to be divided into 2 triangles.
3X Subdivision radio button - divide every triangle (or every selected triangle) into three triangles.
Move Vertices checkbox - specifies whether to allow vertices (triangle corners) to move during the refinement.
Fix Boundary checkbox - specifies whether to allow natural boundaries to move during the refinement.
OK button - performs the refinement, saves the object to the Model Manager, and closes the dialog. If necessary, use Ctrl-Z un-do the change even after closing the dialog.
Cancel button - terminates the dialog without modifying the mesh.