This was my first attempt at a major alteration to a pair of jeans. Although I didn't think to take any before photos, I found another pair of the same jeans and so have pictured them side by side in the first photo. The process was as follows:
Firstly, I took the measurements of the pair in question and of another pair that I liked the cut of. Then, I worked out from them the width that I needed to take off the leg at the cuff, knee, thigh and groin, adding on a couple of centimetres to account for the webbing (see later). I drew with a disappearing marker pen the outline of the area to be removed (on the inseam), and then cut it out of each leg. The trick to making the legs again (without formal training or guides) was to use iron on webbing (generally WonderWeb brand is the best I've found so far) to reattach the inseam of the legs, working upwards until I had almost reached the crotch.
Then, I hand stitched up the place where the fabric met, to give it some more hold, and then went over the crotch (I found it hard to do the crotch with webbing, and found it most exact to simply hand stitch the area. After trying them on to make sure they fitted satisfactorily (which, maybe amazingly they did),
I moved on to the decoration. I had wanted to turn them dark red, but since they were already a darkish grey they ended up a kind of deep wine colour, which I was in fact happy with. To dye them I tried a hand dye from Dylon first but didn't get great results, possibly as the fabric was too heavy for one packet or there wasn't enough salt. After that I tried one of their machine dyes, and the results were uniform and excellent. Also, despite my worries it didn't dye everything in the machine afterwards.
I used hand coloured iron on patches on the back pockets, and as you can see from the final picture a few small ones in spots when my beginner's stitching wasn't quite holding. Since then, I've worn them quite a few times and they have held together fine, ending up with an interesting looking pair of jeans that I am very happy with.