I would suggest you do the following: edit the template of the NumericUpDown control and switch the x:Names of the RepeatButtons in the template. You could easily edit the template of the NumericUpDown control using Blend Expression. Just drop a control on the design surface, right-click it and choose from the menu Edit Template-> Edit a Copy
. Blend will generate all the needed resources.
Please let us know if you have further questions.
the Telerik team