var User = sequelize.define("Users", {
    username: DataTypes.STRING,
    password: DataTypes.STRING,
  });

  var Role = sequelize.define("Role", {
    role: DataTypes.STRING
  });

  var UsersRole = sequelize.define("UsersRole");

  User.belongsToMany(Role, {through: UsersRole});

models.Users.findAll({
    where: { id: req.params.id },
    include: [{ all: true }]
}).then(function(dbUser){
    dbUser[0].Roles[0].updateAttributes({
            RoleId: req.body.role,
        },
        {
            where: { UserId : req.params.id }
        }
    ).then(function (result) {...