No digital picture, regardless of format, can be enlarged without introducing visible blurriness or graininess or distortion.
Also, generation loss (shows up as additional blurriness or graininess or distortion) will occur each time a digital picture is resized. So save digital pictures as-is when you get them. If all you need to do is resize it, resize it once to the new desired size. If you didn't get it just right, start over with the original.
If you need to edit the picture, do the edits prior to resizing. Save and keep the original size edited version, which will probably be in BMP or GIF format. Then resize it once to the new desired size. To make a new version with additional edits on top of the first go round, go back to the original size edited version.