Отредактируйте шаблон (используйте Blend или, если у вас нет blend, сделайте это следующим образом: .NET 4 управляйте шаблонами по умолчанию без Blend )
Это шаблон управления по умолчаниючасть стиля кнопки ленты:
<ControlTemplate TargetType="{x:Type ribbon:RibbonButton}">
<Border x:Name="OuterBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="{TemplateBinding CornerRadius}" SnapsToDevicePixels="True">
<Border x:Name="InnerBorder" BorderBrush="Transparent" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="{TemplateBinding CornerRadius}" Padding="{TemplateBinding Padding}">
<StackPanel x:Name="StackPanel">
<Image x:Name="PART_Image"
RenderOptions.BitmapScalingMode="NearestNeighbor" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
Height="32" Margin="{DynamicResource {ComponentResourceKey ResourceId=LargeImageMargin, TypeInTargetAssembly={x:Type ribbon:Ribbon}}}" Source="{TemplateBinding LargeImageSource}" VerticalAlignment="Center"
Width="32"/>
<Grid x:Name="Grid" HorizontalAlignment="Center" VerticalAlignment="Center">
<ribbon:RibbonTwoLineText x:Name="TwoLineText" HorizontalAlignment="Center" LineStackingStrategy="BlockLineHeight" LineHeight="13" Margin="1,1,1,0" TextAlignment="Center" Text="{TemplateBinding Label}" VerticalAlignment="Top"/>
</Grid>
</StackPanel>
</Border>
</Border>
Измените это в соответствии со своими потребностями, например, вы можете настроить ширину и высоту изображения в соответствии с границей:
<ControlTemplate TargetType="{x:Type ribbon:RibbonButton}">
<Border x:Name="OuterBorder" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" Background="{TemplateBinding Background}" CornerRadius="{TemplateBinding CornerRadius}" SnapsToDevicePixels="True">
<Border x:Name="InnerBorder" BorderBrush="Transparent" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="{TemplateBinding CornerRadius}" Padding="{TemplateBinding Padding}">
<StackPanel x:Name="StackPanel">
<Image x:Name="PART_Image"
RenderOptions.BitmapScalingMode="NearestNeighbor" HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
Stretch="Fill" Height="{Binding ElementName=InnerBorder, Path=ActualHeight}"
Margin="{DynamicResource {ComponentResourceKey ResourceId=LargeImageMargin, TypeInTargetAssembly={x:Type ribbon:Ribbon}}}" Source="{TemplateBinding LargeImageSource}" VerticalAlignment="Center"
/>
<Grid x:Name="Grid" HorizontalAlignment="Center" VerticalAlignment="Center">
<ribbon:RibbonTwoLineText x:Name="TwoLineText" HorizontalAlignment="Center" LineStackingStrategy="BlockLineHeight" LineHeight="13" Margin="1,1,1,0" TextAlignment="Center" Text="{TemplateBinding Label}" VerticalAlignment="Top"/>
</Grid>
</StackPanel>