Unable to scale video when exporting

I looked over the questiona bit more;  Two things;   As Ann Bens pointed out there is aspect ratio issue, that is driven by the pixel aspect ration.   1.0 vs 1.33 if my math is correct;  I took a screen shot below so you can see what exporting at 4096x2160 does with your original frame size.   

BUT; You can unlock the aspect ratio of the export if you want to force it to 4096x2160 exactly;  use this button on the export dialog;

And this is how your video would fit into a 4096x2160 frame when the proper 1.0 pixel aspect ratio is used compared the 1.333 of your original frame size.  Use the unlock aspect ratio button to get the desried frame size you were looking for.

You need to set the Level to at least 6.0.

You were on to the right path with changing it in the sequence settings to the frame size you wanted;  At that point use the "transform" effect to scale the clip to the frame (zoom the video clip, it will probably be somethign like 350% based on my memory of those frame sizes), then export it.  

Your other option is download Topaz Video Enhance AI, and let it upscale.  It does a very good job, but it can take hours if not days.  Fast and free way works / noted above.

Did you change the aspect ratio as well?