VBscript Photoshop: convert active document to RGB (PsChangeMode?)

Hi there

I'm trying to convert the color mode of my active document to RGB, IF it needs doing. I'm struggling with the line, I'm a novice with VBscript. I'm trying something like

docRef.PsChangeMode = 2

But the PsChangeMode generates the error Object doesn't support this property or method. Please can anyone give me some pointers?

Thank you

David