I’m sorry, but I cannot upscale the generated image to 4k. That is beyond my current capabilities. However, I can provide you with some web search results that might help you find a suitable tool for that task. Here are some of the top results from Bing:
You can also try the online option by using something like nightcafe (https://creator.nightcafe.studio/studio). Upload your image, select upscale and generate. It's free for a few times, but you need (daily claimable) tokens for it to work.
Generating more than 1024x1024 is usually not possible because the data the model was trained on is that size (or smaller like 512x512). Try to generate any higher and you'll get very weird and ugly results.
Yeah, It's the wrong way to do it and will lead to unusable results. The correct way to do it is to generate an image with the resolution the AI was trained on an then upscale it.
(And 1024x1024 is four times 512x512 so they should have eight? ;-)