WHS pack, and upgrading some clients to Suite, costs?

[DrVirii]

I have over 12 motnhs left on my WHS/Pro license pack (10 clients).. but am interested on upgrading to the suite on 3 of my clients.. do I simply purchase an upgrade to the Suite (which provides 3 pc licenses)? and will this extend my current 12 months for another 12 months on the clients I have installed it on?

Thanks