I get your confusion, but it really does work. You've been knitting in the round. You are going to continue doing that, exactly as you have been. Here's what happens: you make the switch when you start a new round. You have been holding a size 5 circ left needle and a right needle. You are going to take one end of the size 7 circ and use it as a substitute for the size 5 right needle. The sweater doesn't know you've switched needles (I'm being serious!-- it'll help to understand this.). As you knit onto the 7, the stitches are being gradually transfered to this new needle (and its connecting cord), and eventually all of fabric will be on the new needle, still in a circle. You are not going to change direction or anything else you're doing. Here are a couple of things you can do to make it easier. Let's assume that when they tell you to switch to size 7s, you are also going to probably stop ribbing and switch to stockinette stitch. You could just knit one row in st st using the size 5s, and then on the next row switch to the 7s, just to make the switch less complicated-- you'd only be switching needles instead of that plus changing the stitch pattern. The other thing, simplest of all, is that if your stitches aren't too tight, is to thread the larger size into the stitches and then just pull out the smaller needles, without knitting at all, and then continue as the pattern tells you, all set with the larger needles size.