WPF

...
public ICommand LoadSomeViewCommand;

public SomeViewModel(IRegionManager regionManager, IUnityContainer container)
{  

  this._regionManager = regioinManager;
  this._container = container;

  LoadCommand = new RelayCommand(new Action<object>(LoadSomeViewExecute), new Predicate<object>(CanLoadExecute));

}
...
private void LoadSomeViewExecute(object obj)
{
  IRegion mainRegion = _regionManager.Regions[RegionNames.MainRegion];
  foreach (var v in mainRegion.Views)
  {
    mainRegion.Remove(v);
  }
  _regionManager.RegisterViewWithRegion(RegionNames.MainRegion, typeof(SomeNewView));

}

private bool CanLoadExecute(object obj)
{
  return true;
}

public SomeView(IRegionManager regionManager, IUnityContainer container)
{
  InitializeComponent();
  this.DataContext = new SomeViewModel(regionManager, container);
}

public SomeViewModel ViewModel
{
  get { return (SomeViewModel)this.DataContext; }
}

...
<StackPanel grid.Row="2">
  <Button Content="Load"
          Command="{Binding LoadCommand}"/>
  ...
</StackPanel>