First of all, I can tell that you have the editor docked: if you had it undocked then there would be a toolstrip or the decoration near the downward triangle would be different.
I can also tell that you are not using New Desktop.
I do not have a solution for the "old" Desktop case. Also, the solution given by @nick does not work for me. For the case of using New Desktop:
In the case of using New Desktop, above the list of tabs, there is a tab that has on it what looks like "" (four vertical marks). To the right of that tab, there will be three vertical dots. Left-Click on the 3 vertical dots. In the menu that comes up, one of the options is "Tab Position". If you hover over that menu entry, a radio-box selector will pop up, with the choices Top, Bottom, Left, Right. Click on Top.
