Normally, player 1 is displayed at the bottom, player 2 at the right, player 3 on top, and player 4 on the left of the game view. If you want to change that, you can do this via user profiles. However, the order of the players will be kept anyway.
If the game users pane is not visible yet, you can make this happen with the following steps:
Press this button on the app bar of the game view to show the list of secondary commands. On a PC, you can use the menu of the title bar alternatively. This menu is more detailed than that of the app bar, so you can reach almost all the panes directly.
If you want to change the position of a player, you can do this with following steps: