To Resize (eventually edit the Height or Width to a higher value) the ContentDialog(s) you need to add the following lines to your App.xaml file and edit the Max values as you wish.

<Application.Resources>
    <x:Double x:Key="ContentDialogMaxWidth">1000</x:Double>
    <x:Double x:Key="ContentDialogMaxHeight">1000</x:Double>
</Application.Resources>