So i buyed this miner from BFL from USA to Europe and of cource i have to pay tax (150 euro).
Now say that i wanna upgrade to those new things, i will have to send it back.
Do i have to pay tax again when those come?
Yes. You'll have to pay tax on the new mining equipment when it arrives.
Second question: If i refuse the delivery of the first one, it gets send back anyway no? that way i wont have to pay tax and shipping.
Or is that wrong?
If you refuse delivery it'll get sent back with no tax. You will most likely still have to pay for shipping though.