[WPF - MVVM - Caliburn.Micro] How can I manipulate the location of my controls?

Question

I'm using WPF, and MVVM with Caliburn Micro (for the first time).

My UI has 2 textboxes that look like this:
]2

Well, each is actually a Dock panel that contains another Dock panel (black thing) and the actual textbox.

Originally, I had 2 function like so:

They are supposed to switch the orientation of the Textboxes b/w horizontal and vertical. I made these functions when I wasn't using MVVM. Now that I am, I don't know how to go on about doing this.