Chance subscription from 1 PC to multiple...

I wish to change my order from 1 PC Premium Security to Multiple Devices Premium Security. I have almost a year left on my 1 PC subscription. Can I change/update my subsciption without losing the money I have paid for the rest of remaining 1 PC subscription and how do I proceed? Or just buy another product, pay for one year and have both subsciptions paid? I didn’t find FAQ answers to this question - or maybe I didn’t search right.
Thanks in advance.

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