I start to put pins where I want the new length of my jeans.
(Already washed and used them folded so I have stretched them to fit me)
Save a little more than an inch and cut.
Folding to use to measure around.
Turn the jeans inside out. The pins still there so you know next where to fold.
Fold 1/2 inch twice and put pins.
Save this part, probably you need to go to the store to buy a matching tread.
I always have difficult to find the right one, have to take something as close as possible.
Set up the sewing machine.
Start inside/back (not so visible)
Make a double knot on the inside.
Sew around, careful over the thick seams!
Sew double for an inch and make another double knot.
Done! For a better look: wash the jeans.