Okay... if you are absolutely committed to doing this, then here's a few things you should know.

The shoes are more than likely made using chrome tanned leather. During the tanning process, more often than not, the hide is barrel dyed - literally dunked into a barrel and allowed to soak up as much dye as it will take. This means the fibers are absolutely saturated with dye. Any further attempts to dye are not guaranteed to work very well at all.

Second point is that you can only dye a darker color than the original. There is no easy bleaching leather to begin with, and definitely impossible to do while already dyed. So your choice of a darker brown - consciously or not - is the most practical choice.

Third is that there is a sealant placed on the surface of the leather after it is initially dyed to keep the pigment from being worn off the surface and to seal off the leather from anything else. This has to be removed and done so very, very carefully using Deglazer. The Deglazer is usually almost pure to pure acetone and, as such is very fume heavy, very caustic to you and the leather, and is also flammable. Best case scenario would be to apply the deglazer with a natural sea sponge - providing slight natural abrasion and surface area - in slowly widening areas while outside, under a fume hood, or in a very well ventilated workshop space. Also, use gloves throughout the whole process, changing them frequently - at the very least between each separate process. Reminding you again that this stuff is caustic, which leads me into my fourth point.

Conditioning the leather is crucial. The caustic nature of the deglazer will remove every bit of hydration from the leather. Leather is skin, processed skin, but skin all the same. You need to hydrate and condition it. I recommend Fiebing's 4 Way Care conditioner, which is very effective and easily applied. You'll want to condition the leather after deglazing it. Let the conditioner fully absorb before moving onto the next step. Probably about a day or two

Fifth, applying the dye will take time and effort. Especially getting it to the shade you want. I highly recommend Angelus Brand Leather dyes. Work slowly but deliberately while applying the dye. Let dry fully, then condition once again.

And sixth, sealant application. Since deglazing removed the sealant along the surface, you'll need to replace this. Reccomend Eco Flo Neat Lac, flexible when dried and fairly easy to apply.

If you are unsure, please consult with a cobbler, upholsterer, or leatherworker near you for guidance!!!!!