You can decide for yourself if you want your data to be stored in the EU or the US. We recommend that you choose the datacenter closest to you.
From the teacher dashboard, press the My Account button in the top right corner. Choose the Account settings button from the drop down menu. Here you have the option to choose where you want your data to be stored. Once you have chosen your data storage location, press SAVE SETTINGS and your data will be transferred.
Moving your data takes a while, depending on how much data you have stored. If you have a large library for example, it might take quite a few seconds for the transfer to complete.