You must have working knowledge of a sewing machine in order to do this. Your bobbin should have the same colour of thread as your main thread. Have your pins and measuring tape handy at all times!
This is an example of "before and after" so you can see what you are aiming for. Here we go!
Figure out how much length you want to take up on your jeans. Fold them up to where you want them. Try them on with shoes to make sure that length will work with your heels, boots, etc. Now pin.
Measure from the inside hem to the fold to see how much you want your jeans shortened. In this example, my BF needs his jeans shortened 3 inches.
Now, this may seem weird but take the length you want off & divide by half & re-pin your jeans so the fold is half the length they were before. In this case, 3 inches has now turned into 1.5 inches.
Then, starting at the side seam, start sewing your jeans as close the the underside of the original hem as possible. Make sure you dont sew your jean leg closed!
You can't even tell I sewed the jeans...that's why it is important you sew close to the underside hem.
This is what it looks like underneath. One straight-ish line.
Now fold the jeans over--right side out! It's up to you whether you want to cut out the extra material on the underside or just iron it in really well.
See? All done...like I said, iron it down and no one will really know that there is a seam there. Who really pays attention to hems anyway? Your jeans will just look snazzy and decently "tailored".