I have upgraded my plan on Leonardo, and it has a upscaler build-in. But it cost around 80 tokes (my recent plan was total or 8,500 tokens a month).

Before that I have used Clipdrop upscaler that cost me 10 USD a month.

While the free upscalers are good, for TV frames with 4K resolution, you need a high-quality upscalling tool that cost money.