Well, Roger from Sheffield, first you decide how far you want to go when transposing. I, for example, changed that mazurka from G to D for better playing on the flute, which abhors low notes. You can do this for free by writing the notes of the old scale above the new:

G A B C D E F# G D E F#G A B C# D

Then every D in the old key becomes an A in the new. And F# becomes a C#, etc. An E minor chord becomes a B minor. A C minor diminished 9th becomes a G min dim 9th, etc.

Obviously, if you do this very much, you will want to get a program to print your stuff. I have a little keyboard by MusicStar (cost abt $60) and a program called EZPIANO which has its quirks but cost less than $100. (don't know if it's still around) It came from a Canadian named Andy Kula

I absolutely love finding and printing music, which I then project on the wall of my living room when my musical friends come over. Ours would be a better world if more people did this kind of thing.