Ruth, here you go. This is how I do the shortening. I am using this BWOF 08/2008 #109 to show you how to do it. This is for a raglan sleeve top so the sleeves look a bit different than your typical set-in sleeve. I added a picture of that too.
This is where I typically shorten my tops. I shorten all the pieces, back included. This top has two piece sleeves.
Here it is after I shorten all the pieces. Be sure to check all your grainlines. All your grainlines should be the same after you shorten the pieces. This is especially important here when it is a raglan top like here. I make a 1/4" fold but, because there are two layers, it totals 1/2". You'll notice the lines don't exactly match up anymore. I just fudge it when I'm cutting.
Here is a typical set-in sleeve. Well, not so typical because it was a half sleeve but you get the idea.
This is what I did at first because it looked more "normal" but this would mess up the grainlines and not shorten it the same compared to the front.
Hope that helps you Ruth.