Lifted from somewhere------------too tired to type
First, ill tell you what a step is. in music one step is the same term as 1 whole tone.
A half-step is also called a semi-tone.
To give you an idea, 1 tone (or 1 step) is 2 frets away on guitar. so if you play the low E string open (just pick the string - dont fret any notes). well, you played the note "E".
1 step up from that (or 1 tone) is 2 steps higher which would be the same string, but the 2nd fret. 1 step up again from that would be the 4th fret.
A half-step is 1 fret away. so if you play the low E string again (no fret, just pick the string) you get the note "E". if want to go a half step higher then fret the 1st fret - now you have an "F" note. a half-step up from that is the 2nd fret "F#" note.
So basically you want to tune your strings down a half step each (called Eb or E flat tuning).
First, tune your low E string (the top "fat" string) down just a little, so it has the same pitch as the 6th fret on your A string (the closest string to the "fat" E you just tuned).
From there, tune all your other strings down a half-step to your E string that you just tuned down. tune them with your E string (which is now Eb since you tuned it down a half step) the way you normally tune them when you have your E string in tune.
I hope that makes sense, if not let me know. you can get a tuner for your guitar that shows you the notes, that would be easier. there are even some digital ones on the web.
Also, when tuning down, you need to first let the string tune down lower than the pitch you want, that way you "tune up" to it, instead of just tuning the string down and stopping on the note. what this does is takes the slack out of the string, if you dont do it then the strings will be trying to "stretch" themselves back up while you are playing - since when you had it tuned in standard tuning (EADGBE) they were stretched to those tones.