Need to replace steam valve in Starbucks Sirena...

Question

How do I replace the steam/froth valve in my Starbucks Sirena and where can I get the parts?I know how to open the unit to get to the valve but don't want to try going any further without good direction. I've searched the web to no avail and haven't had a chance to contact Saeco directly yet.

Any and all help greatly appreciated. Thanks