You'll need to set up a new Roku account when you reach Portugal. Before you leave the US cancel any premium subscriptions you have through Roku, as you won't be able to access them on your new account and you don't want to keep paying for them.
Don't forget to take your Roku remote. You won't be able to set up without it and it may be difficult to find a replacement remote there.
When you get to Portugal and get established with a local internet provider, also establish a Portugal based email account.
Now hook your Roku up to the tv and do a Factory reset on the Roku. (With it plugged into the power source, push the Roku reset button for a minimum of 30 seconds no matter what you see on the screen.). When the Roku boots up its memory will be cleared and you'll have to set it up as if it were a brand new unit. In this process, create a new Roku account with your Portuguese email address. When completed you'll be linked to your new Portuguese account and will be able to get whatever channels are available there.
If you have paid subscriptions taken out directly with the channel supplier you should still be able to add and use them there, provided they operate in the Portuguese market. Just log into them with the same credentials you used in the States (i.e. your US email and password for each service.). If they are not available in Portugal you can log into their websites and cancel your subscriptions to them.
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