I fount this site, very helpful , it describe step by step the process.
http://daciaray.com/?p=38
Step 2: Cuff the jeans. I wanted to take two inches off my hem, so I measured one inch out from the original hem line and pinned. (Do not include the distance from the hem to the end of the jean in your calculations.)
Step 3: Pin around the rest of the cuff, taking care to measure each time you pin.
Mind the seams while youre pinning. Make sure that the stitching lines up at each seam.
Step 4: Its time to stitch. You want to place your needle and continue sewing right next to the original hem. Stitch on the right side of the hem, or the side farthest from the bottom of the jean. Sew all the way around the cuff. Be sure you dont sew through both front and back sides of the jeans (making it so that the foot hole is sewn shut)!
You can either cut the excess off, leaving about a half inch for fraying, or iron the extra material in.
Turn the leg right side out and press the new seam flat, revealing the old hem.
Voila! No more slouchy, unflattering leg.