How can I make the music larger?

When you print the music and you think the note heads are too small we recommend using Adobe Acrobat Reader because you can fine-tune the print size.
 

 
Usually you'll get the best result by selecting the "Actual size" button. The only reason not to select "Actual size" is if your printer clips the margins. In this case you'll want to use Fit.

If "Actual size" is still too small you can push the limit a bit by selecting the "Custom Scale" and raising the number a little higher (probably you won't be able to go above about 105%) until your printer doesn't clip anything that you deem important.
 
Another approach (assuming you don't have a large format printer) is to take your pdf to a local print shop and print onto a larger form factor paper (e.g. A3). This will make the print a LOT larger and it should still have very good resolution.