First turn your sweater inside out and lay a top you like over it, then mark the new size with pins. You can actually try the sweater on at this point just be careful not to get stuck!
Using the pins as a guide, draw a stitching line with a black sharpie. Sew over the lines using a stretch stitch. Trim seam.
Now cut the sleeves to your desired length. I made three quarter length sleeves.
Cut the cuffs off the sweater leaving about 1/4 in. extra above the cuff to provide a seam allowance when you sew it back onto the sleeve. If the cuffs are too loose you can trim them to make them smaller. You will want the cuffs to be a little smaller around than the sleeve.
Stitch the ends of the cuffs together, then pin them onto the sleeves stretching the cuffs to fit. Lastly sew them on.
I also refashioned the corduroy skirt I'm wearing. Before, it had stuck out strangely at the hips. So I took that in and hemmed it shorter. Although I didn't particularly mind the length, the skirt was pretty narrow at the bottom and was annoying to walk in.