How can the instrument be changed without entering new scores?

I selected violin as the instrument when creating scores. Of course, the sound when played was that of the default piano1.sf2. After installing the Gen MIDI Unison, I didn't like the violin sound and tried to change back to the initial default sound but Vista Windows Explorer couldn't find the file when searching the hard drive. When I tried changing the instrument in the scores already created, the program presented a new blank score. I tried copying the score (Select All and then Copy) and then pasting it into a new blank score that had piano as the instrument, but it wouldn't paste. I tried reinstalling the program over the old hoping the default sound font would be reinstalled, but the Unison sound font was stil there. I can't think of anything else to try... Is there a way to do this?