Is it possible to change the size of a project from 19:6 to 9:16?

 I'm not sure, but I bet you can select all elements in the timeline, COPY, then close the project, create a new project with a different proportion, and then paste the elements into it. If it works, you will need to rearrange things to fit the new proportions.

Note:  As discussed in a different thread, the 9:16 project selection does  not actually produce a true 9:16 ratio at the moment. SO if you want a true 9:16, you might have to choose 16:9, rotate all of your elements 90 degrees, render your finished video, then use a video editing program to rotate the finished video 90 degrees the other direction.

-Mike (videoscribe user)