Because the myCloud Desktop client synchronises your data with myCloud.ch, thereby keeping it up to date at all times, it is not advisable to disconnect your myCloud account and thus log yourself out. If you wish to do so anyway and connect a different myCloud account, you can log out by clicking the gear icon at the top right in the myCloud Desktop client. You should now see the profile view, in which you can click the «Connect another account» button. After you click the button, a confirmation window will appear again before you are successfully logged out.