Follow the following steps to edit control template or access it.
1. Open your .xaml file
2. Right click on your control
3. Click on Edit Template, then click on Edit Copy.
4. Then you can decide whether you want apply this template to only this control or apply all existing. Also Where you wanna define it
5. After this you will see the xaml code for that control, you can edit it the way you want !!
In Xaml go to your control, I have taken “Button” as my control
In Designer Right Click on the Button Control -> Edit Template -> Edit Copy.
Do you want to apply to all Buttons ? or create a new Style with custom Name(key) use it only one certain buttons ! Also Where do you want to define this style ?
After you hit Okay you will see the Button Style Template !! Enjoy !!