If you want to take your denim from dark to light, bleach can do the trick -- but it can also result in colors that you didn't anticipate. It all depends on the quality and the fibers of your jeans. When it comes to bleaching, take it slow. Monitor the bleaching process closely to make sure you're stripping away the amount of color you want. Otherwise, you could do more than change the color of your jeans -- you could accidentally burn holes in them.
Change into clothing that you don't mind getting splashed by bleach. Lay newspapers on the floor near your washer and dryer in case of spills, and place a basin -- such as a plastic tub -- on top of it.
Fill your basin with one part water and one part bleach. Avoid a more highly concentrated solution; it may get you faster results, but it's significantly more corrosive and less predictable. You may inadvertently burn holes in your fabric.
Put on rubber gloves and submerge your jeans in the solution without balling them up. Arrange the jeans so that they are evenly exposed to the bleach solution or you'll end up with patterns and fold marks in the fabric.
Check on your jeans after 20 minutes, which is about the earliest that they'll start showing results. Don't pull them out until they are about as light as you want them to be at the finish. After another 30 minutes, check again to gauge how quickly the solution is working. Once you are satisfied with how light they are, remove them from the solution and wring them out over the basin to drain excess liquid.
Carry your jeans to the washing machine, holding them over the newspapers you laid down earlier in case of drips. Prevent the jeans from pressing against your clothing.
Run your jeans -- alone -- through the washing machine twice without using detergent or fabric softener, which can cause yellowing. This rinses out all of the bleach.
Hang your jeans to dry to avoid the high heat of the dryer, which can cause yellowing. Once they have been rinsed in the washer and dried, the bleach has set and your jeans are ready to wear.