Not sure if you have this option in the studio version, but if you right-mouse-button click on the video and open up the Properties window, you can set the aspect ratio there to 1.2121.
If that's not available, you can open up Pan/Crop, uncheck "maintain aspect ratio" and check "stretch to fill frame".
Great, I expanded the frame to 16:9. Now I tried to render it - and surprise, in Render as popup the button Render is disabled whatever I select in the list. So ... how can I save changes to the original file?