VBA - Adjust selection to preset size

Greetings all,

I'm having a little trouble with some code. I want to set a shape to 5'x5' using the current selection. What I have currently is below and it's not reading it. I'm not sure if .Size just isn't a valid argument?

Dim OrigSelection As ShapeRange
    Set OrigSelection = ActiveSelectionRange
OrigSelection.Size 5#, 5#

If anyone can point me in the right direction or show me where I've gone wrong it would be appreciated.