private void DecrementValue()
    {
        //Value--; <-- Don't do this

        // Do this instead:
        ValueChanged.InvokeAsync(Value - 1);
    }

<UserControl x:Class="MvvmLight6.Views.Menu"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
   xmlns:vm="clr-namespace:MvvmLight6.ViewModels" mc:Ignorable="d"
   FlowDirection="RightToLeft" d:DesignHeight="300" d:DesignWidth="400">
   <UserControl.Resources>
       <vm:MenuViewModel x:Key="vmMenuViewModel" />
   </UserControl.Resources>
   <StackPanel DataContext="{Binding Source={StaticResource vmMenuViewModel}}">
       <HyperlinkButton Content="صفحه یک" Margin="5"
                        Command="{Binding DoNavigate}"
                        CommandParameter="/Views/Page1.xaml"
                        />
       <HyperlinkButton Content="صفحه دو" Margin="5"
                        Command="{Binding DoNavigate}"
                        CommandParameter="/Views/Page2.xaml"
                        />
   </StackPanel>
</UserControl>

using GalaSoft.MvvmLight.Command;
using GalaSoft.MvvmLight.Messaging;

namespace MvvmLight6.ViewModels
{
public class MenuViewModel
{
    public RelayCommand<string> DoNavigate { set; get; }

    public MenuViewModel()
    {
        DoNavigate = new RelayCommand<string>(doNavigate);
    }

    private static void doNavigate(string url)
    {
        Messenger.Default.Send(url, "MyNavigationService");
    }
}
}

<UserControl x:Class="MvvmLight6.MainPage"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
   xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
   xmlns:sdk="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls.Navigation"
   xmlns:usr="clr-namespace:MvvmLight6.Views"
   mc:Ignorable="d" d:DesignHeight="300" d:DesignWidth="400">
   <Grid x:Name="LayoutRoot" Background="White">
       <Grid.ColumnDefinitions>
           <ColumnDefinition Width="*" />
           <ColumnDefinition Width="268" />
       </Grid.ColumnDefinitions>
       <usr:Menu Grid.Column="1" />
       <sdk:Frame Margin="5"
                  Name="frame1"
                  HorizontalContentAlignment="Stretch"
                  VerticalContentAlignment="Stretch"
                  Grid.Column="0" />
   </Grid>
</UserControl>

using System;
using GalaSoft.MvvmLight.Messaging;

namespace MvvmLight6
{
public partial class MainPage
{
    public MainPage()
    {
        registerMessenger();
        InitializeComponent();
    }

    private void registerMessenger()
    {
        Messenger.Default.Register<string>(this, "MyNavigationService", doNavigate);
    }

    private void doNavigate(string uri)
    {
        frame1.Navigate(new Uri(uri, UriKind.Relative));
    }
}
}