Unblurring is not enlarging
An enlarger makes a picture bigger. If the picture was blurred when it was taken, a bigger picture is a bigger blur. Here is how to tell the two problems apart.
Two problems that look alike
A size problem: the picture is sharp at its own size and simply has too few pixels for where it is going. Look at it at 100% — edges are crisp, letters are readable, it is just small.
A blur problem: the picture is soft even at 100%. Focus missed, the camera moved, or something smeared it. More pixels will not fix that, because the detail was never recorded.
Check at 100% first. If it is sharp there, enlarge. If it is soft there, enlarging only makes the softness bigger.