If I understand correctly, you want to show image with size 32x32 in CommandBarButton element. If so, here is how you can do that:
1. Use image with size 32x32.
2. Set the MinSize if you want to have space between image and borders of the button.
.commandBarButton3.Image = global::CommandBarButtonDefaultSize.Properties.Resources.Button_Next_icon32x32;
Hope this helps. Feel free to ask if you have any additional questions.
the Telerik team