Under the Change a User's User Group section, enter the Username of the user and press Enter on your keyboard. (If the user's account hasn't been created yet, first register the user account.)
On mobile devices and in some themes, click the (main menu) icon located towards the top left corner of the page. Skip this step if you don't see the icon.
Click the Members link.
Check the checkbox next to each member for which the user group has to be changed.
Click the icon located towards the bottom-right of the page.
Click the Change user groups option from the dropdown box.