These are some former trouser jeans of mine that had turned into high waters. Over time, so many of my jeans have gotten too short in the wash. I've since learned (thanks, Paula!) how to avoid this, mostly: Don't ever dry jeans in the machine, only hang them to dry (yes, very obvious but wait for it:) then AFTER they are dry, put them in the dryer to become wrinkle free and soft.
So, as I was saying, since these were unwearable anyhow, I cut them off into long shorts using the original hem to make them look more finished. This worked fine because the hem at the bottom was as wide or wider than the leg at the knee. If your hem is not flared, you may not have enough original hem to attach to the leg. Be sure to check this first before you do anything crazy.
First step is to try them on. Mark the length you want them to be when finished. Take them off, lay them flat, and subtract the width of the original hem at the bottom of the leg. Then add .25 inch. Make a mark at this new measurement on both legs and cut those babies off.
Also cut off both hems from the bottom of the legs. Make sure you leave some extra fabric above the hem.
Good idea to use a heavy needle in your machine and also jean thread, which is slightly thicker and stronger than regular thread.
Turn your hem pieces inside out and trim them down so there is about .25 inches of fabric above the hem.
Pin them on right sides facing and with raw edges even. If the hem is too wide for the leg, snip it open at the inside seam and overlap it.
Sew right next to the hem all the way around the leg and finish the raw edges by overlocking or zig zagging them.
This is what it looks like after sewing and overlocking, but before pressing. You'll definitely want to press it well with a hot iron so the new seam lays nice and flat. You could also topstitch around it about 1/8" above the hem, catching the seam allowance underneath to add a finishing touch (I was too lazy).