[JasonB]

Another option for enlarging images without the usual problems of pixelation and/or loss of detail, is Upscayl. 

I certainly can't put this into the 'tried and trusted' category, since I only downloaded it a couple of days ago, but the results are very impressive, and it's a doddle to use.

It's cross platform and open source, and there are desktop and cloud versions. The desktop download seems to be free, the cloud version comes in a number of varieties with different pricing plans. I haven't yet bumped up against any restrictions on the free desktop version, but I haven't used it extensively.

I've seen it recommended highly, and I can see why.