Check the fine print (may need a magnifying glass) on the charger you plug into the wall. It should show you the required input voltage. If it only lists 110 or 120 vac, don't use it where the service is 240 vac.
Most of us have a pile of these things lying around from phones and other devices. Most of them will adapt to either voltage -- again, check the fine print. Just be sure the amperage is at least as high as the original Roku device (mine are all 1.0 amp).
You may also need a plug adaptor, as the physical arrangement of the plugs and sockets in different world areas may not line up with the two parallel flat prongs used in the US.
Do note, though, that various Roku channels may be specific to certain geographical areas, so you may not be able to get the same channels you can get at home.
THANKS! It says 100 to 240, so I'm good to go.
@berts Is that information on the Roku box itself? I'm also overseas (South America) and before I buy one I wanna make sure I can use it. My voltage is 220V, but if it does say 100-240V on the box, then I'm good, too. Thanks!