code: public static void changeColumn (Connection conn, String table, String cname, String cdef)
          throws SQLException
      {
          String update = "ALTER TABLE " + table + " CHANGE " + cname + " " + cdef;
          PreparedStatement stmt = null;
          try {
              stmt = conn.prepareStatement(update);
              stmt.executeUpdate();
          } finally {
              close(stmt);
          }
          log.info("Database column '" + cname + "' of table '" + table +
                   "' modified to have this def '" + cdef + "'.");
      }
docs: Changes a column's definition. Takes a full column definition 'cdef' (including the name of
  the column) with which to replace the specified column 'cname'.
  
  NOTE: A handy thing you can do with this is to rename a column by providing a column
  definition that has a different name, but the same column type.