How to upscale video with static images from 1080p to 4k?

[XilburQost]

I have a series of 1080p videos I created in Premiere Pro that are basically slide shows of static images with various transition effects. As many of the source images in the video are 3k to 4k pixels, I was hoping there would be a simple process to increase the outputted video to 4k in order to take advantage of the extra available image pixels. Unfortunately, for a noob like me, I am not yet successful. Is there a simple process to accomplish this?

I attempted to scale the video up to 4k by selecting the sequences (static) images and going to Sequence > Video > Frame size and changing it to 3840x2160, but unfortunately, the result was just that: larger frame size with images floating on a black background, still scaled to the original 1080p video. 

If I right-click a sequence, there is "Scale to frame size" and "Set to frame size," but again, neither accomplishes what I want: increase everything by 200%. I think I could probably resize each sequence manually, but that would be a lot of work that I'm hoping Premiere Pro can do more easily. Thanks. Premiere Pro 22.2, Windows 11

[Ann Bens]

Original UHD framesize is lost after exporting to 1080p.

If you want to properly upscale you need the original images.

[Mike Dziennik]

It sounds like you have the original images in sequences - you're not talking about scaling an exported file?

There is an option in the sequence settings called: 'Scale motion effects proportionally when changing frame size'.

Unfortunately it doesn't really work when scaling up your sequence - it would be nice if it did.

If you had used 'Scale to frame size' on the images in yoru original sequence, then they would appear consistent in a larger sequence - I assume you did not do this and so the only option really is to go through and double the values of your 'scale' keyframes. 

[XilburQost]

To clarify, yes I do have the original images and they're still available to the project. Barring a global solution, I'll see if I can't select each image sequence and scale them 200%. Hopefully this won't be too difficult. Thanks for the responses. 

[XilburQost]

I've stumbled onto a workable solution:
1) Start a new Premiere project

2) Import a 3840x2160 image and drop it into the timeline

- this sets the video previewer to 4k)

3) Import all the sequences from the 1080p project

- sequences are imported into the Media Browser

4) Select all the sequences and drop them into the Timeline

- the images/sequences are compiled into a single sequence

5) Select the sequence on the Timeline and go to Effect Controls > Video > Scale and change it from 100.0 to 200.0
6) Voilà! Everything is correctly scaled to 4k, including the text titles, without loss of quality.

[Ann Bens]

- the images/sequences are compiled into a single sequence

5) Select the sequence on the Timeline and go to Effect Controls > Video > Scale and change it from 100.0 to 200.0

By @XilburQost

Anything upscaled from 100% to 200% will cause image quality loss.

[XilburQost]

Ann Bens, alas, you're correct. The 3k-native source images are still rendered at the same 1080p resolution in the new project upped to 4k. I went into this assuming that having upped the resolution of the new project to 4k, that it would then load and render the same source images at their native 3k resolutions, but that does not appear to be the case. 
Again, there is a lot of complicated layering and transition effects in the original 1080p version, and I was--hoping--that upscaling to 4k without having to revisit these effects would be straightforward.