I got an idea that my black linen dress was roomy enough for a jumper, so started looking for something of a thin fabric that I could wear underneath. I found a very thin Anthropologie tee, but the scoop neck was rather low. When I tried it on with the dress only the sleeves were visible; I wanted to see if I could raise up the neck area a little. A whole inch, actually, was what it needed.
I know the proper way to take up a shoulder seam is to rip out the stitches at the shoulder, but that's too much work - also, when your top is fitted that could make the armholes too snug. But I've accomplished it the lazy way many times and it always works for me. I needed to take it up one inch. So, starting at the neckline end of the shoulder seams I stitched it at an inch, and then as I approached the shoulder edge, angled it so the seam disappeared into the existing seam. Does that make sense?
Can you see in this picture that on the left side (where the shoulder is) the stitching line I made is at the original seamline? But on the right, where the neck edge is, I've gone diagonally to take it in an inch at that end of the seam. It's a bad photo, I know. But I'm hoping you're getting what I'm saying.
I always baste it first, then try it on again before sewing with the machine. So that's what I did, and it was an improvement, so I finished it up, then trimmed off the seam allowance and zigzagged (even though knits don't fray). It brought it up to where at least some of the neckline was slightly visible beneath the jumper.
As you can see, it looks fine - you'd think it would look funny after taking it up in that angled way, but it doesn't. Even so, that's why I always baste first and make sure it looks all right. I have done this many times over the years for a gaping neckline, which is a problem for me and my narrow shoulders - it helps. So maybe if you have that problem it will help you, too.