The only way to enlarge them and get any kind of result is to use the Resample dialog. I wouldn't hope for much in the way of results. You only have a finite amount of data. Enlarging requires more data to maintain existing detail. My experience has been that images can be enlarged to 130-150% of their original size with resonable results. This means if you want to get a 2x2 inch image enlarged you might be able to push to 3x3 inches at the same (screen) resolution. If you are going to print, you need to get to at least 150 ppi which means, keeping your image dimensions identical, you would have to go over 150%.
You would be much better served, if possible, sourcing a higher resolution image.
I hope you were able to solve your problem. I love high-quality images, especially when it comes to online sources.
There are a heap of tools to do this, including free online tools. And I think the last version of CGS had tools for enlarging and removing jpeg artifacts.
Exactly which of them works best... you can get back to us on that. duckduckgo.com/