You can achieve
your requirement by accessing the button through VisualTree and changing
its width. We have created a simple sample based on your requirement please
refer to the sample for your reference.
CodeSnippets
RepeatButton button1 =
updown.Template.FindName("upbutton", updown) as RepeatButton;
RepeatButton button2 =
updown.Template.FindName("downbutton", updown) as RepeatButton;
button1.Width = 30;
button2.Width
= 30;
Attachment:
Updown_386f4f11.zip