var model = new GroupDeleteRequestModel()
{
    Groups = new GroupDeleteModel[] 
    { 
        new GroupDeleteModel()
        {
            ProntoID = "MyAccountName"
        }
    }
};
var results = serviceClient.DeleteGroups(sa, model);
if (results.IsSuccessful)
{
    //do work...
}
else
{
    //handle error
}

Dim model = New GroupDeleteRequestModel() With { 
	 .Groups = New GroupDeleteModel() {New GroupDeleteModel() With { 
		 .ProntoID = "MyAccountName" 
	}} 
}
Dim results = serviceClient.DeleteGroups(sa, model)
If Not results.IsSuccessful Then
    'do work...
Else
    'handle error
End If