NoteYou can only merge
               layers at the same subdivision level.
            
          
         
            - In the Layers window,
               hide any sculpt layers you don’t want merged. For more information,
               see 
                        Hide or show a sculpt layer.
               
Any remaining visible
                  layers on the same subdivision level will be merged.
               
             
            - In the Layers window,
               select the Layers window menu ( 
 ), and
               select Merge Visible.