To get the chords for a song in a new key when you already know the chords in another key.

1. First, you have to know what key you are playing in and what sharps or flats are in the you want to go to. If you don't know these, this page shows you, down at the bottom: http://www.smu.edu/totw/keys.htm

2. Write out the notes for the old key. Underneath that, write out the notes for the new key. For example:

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

Like magic, you can look up and down and see what the new chords are. Where the old version has an F chord, the new will have a C chord. Where the old has a C, the new will have a G. B becomes F#.

If there are other elements to the chords, keep them as is. For example, if there is an A minor, it becomes an E minor. B7dim6susp (if there is such a thing) becomes F#7dim6susp.