How to update firmware on a Sirius model S50?

[RickS50]

I have a new (purchased on eBay) Sirius S50 satellite radio that I got to replace one that died. Even though it was new, it was from old inventory that had an early version of the firmware installed. I would like to update it with the latest firmware developed but the model S50 is no longer supported by SiriusXM. Does anyone know where I could find the latest firmware and a procedure to installing it?