Adding Licenses? Buying New Product?

I have a 3 pc license for Bitdefender Internet Security that will expire in 177 or so days.

Recently I bought a 4th pc...

now here are my options (as far as i can tell)

buy 1 license for $39.99usd/1 yr

buy 3 license for $49.99usd/1yr

buy 5 license for $79.95usd/1yr

buy 3 license for $69.99cad/2yr - please note the currency is different here (I live in canada)

now the last option is clearly the best option value wise to protect 3 of my pcs but I am still out in the cold over that 4th pc

my mother however has a computer in a different house...

Can I buy 2 3 license packs and apply 1 license to her computer or do the licenses ?

Is it possible to *upgrade* to a greater license (as in go from a 3pc to a 5pc license) and if yes how would I go about doing this?

I am looking to get the best value for my money, but I don't know if these are all my options

I tried contacting bitdefender directly about this a couple of times but haven't gotten replys (I don't believe that my questions are getting through to support), I was running a bit defender trial account on my latest computer but that has expired.

Thanks for the help