Is this a show? Corporate meeting use? Projection? More info to clarify your request.
What is final use?
Taking 1920x HD signal to a 4K version will never hold quality via video at full size on a 100% LED or Flatscreen. You don't have the resolution to go upscale, but depending on projection, the resolution may be enhanced by the TV or Projection systems.
I'm not sure what you really want because it's only possible to resize and reframe the video to your PAL specs, and hope it looks good on screen from far. They human eye and the tech will cheat and therefore offer a visual illusion of enough information to be viewed. But I can't promise that.
If the frame doesn't match proportionately, top and bottom may be trimmed or cropped a bit.
So I don't know what anyone else is selling you, but you need to have 4K editing software to upscale it.
I can edit and resize, but I can't promise due to not knowing what you'll play it on, and I can't tell till I see it either.
1 Day of edit suite and render at 4K - depends on length of video.