Even for sheet music that you get as a low resolution .gif, or another digital form, if you print it the ink/toner often will "fill in" between the pixels so that you get a fairly continuous spread of ink on the dots. If you scan the printed page at a somewhat higer resolution than the original file, you may be able to enlarge it enough to "print it bigger" with a little better results. It's not really a certainty that this will work better than just enlarging from the original file, but I've found many files where it sort of works (and of course some others where it doesn't).

It's a peculiarity of nearly all the graphical file formats that if you have a program that can do it, enlarging by 10% at a time, repeating until you get to the size you want, will usually give you a "visually better" enlargement than if you do it all in one step. When you do it in many steps the picture usually falls apart due to "fringing" instead of by the pixillation you get with single-step enlargement, and sometimes a "Gaussian blur" or "Unsharp Mask" will clean the fringes up some. There are limits to how far you can go either way, of course.

If you have scores "on paper" a difficulty you may run into is that most "music paper" is larger than the 8.5" width that the majority of scanners or printers can handle. There are a few multipurpose machines available that scan and print, that can handle US "B" size (11 x 17 inches) or A3 that's a about a half inch wider but a half inch shorter, and those will handle the common "music book" pages. They're a little more expensive than the ones generally available, perhaps 2 to 3x the price of the promoted ones, and for the usual "letter size" scan/print operations they tend to be quite a bit slower; but you should find the few out there with a search for "wide format" printers or scanners or multipurpose etc. (If you search for "large format" you'll only find the "commercial" stuff that starts in the kilo-buck price range - a search engine peculiarity(?))

John