Anyway, last year when everyone was wearing white jeans, I considered bleaching them bright white, and then I never got around to it. Then this year, pastels are suddenly popping up everywhere, and now I'm glad I didn't touch them. But they did need a bit of updating and "casualizing."
Step 1: turn your pants inside out and put them on. Pin along the inside of one pant leg, marking how skinny you want them (I was going for a slightly looser skinny pant, rather than making them jegging-tight). Carefully remove the pants.
Step 2: Many pants like these have a double seam on the inside of the leg, as seen in the two photos below:
Unpick the seam marked "bottom seam," as seen below. This will be the one closest to the serged edge (as you can see), and will NOT make a hole in your pants if you unpick it. If you suddenly have a hole, you've unpicked the wrong one.
I only unpicked a few inches because the seam to skinnify the pants angles away from these seams and they won't be in the way after a few inches of sewing. But to begin your "skinnifying" seam, you will start sewing on the original "top seam," so you need at least a few inches of access to it.
Step 3: Once your extra seam is unpicked, sew along your pinned line. Begin your seam at the first pin, sewing over the original inside pant seam for a few stitches, then angling gradually away to make a nice angle down the leg toward the ankle.
[try on the pants at this point, if you'd like, to make sure the seam is straight and they are skinny enough for you]
Step 4: Cut off the extra fabric about a centimeter away from the seam you just made (the photo below is a bit deceiving. That crease is not the seam, it's just an accidental crease. The seam is 1 cm to the right of the scissors):
Step 5: Zigzag or serge the raw edge so it doesn't fray.
Step 6: Turn the pants inside out again and repeat steps 1-5 on the other leg.
Step 7: (optional) roll the pant legs up for a more casual look. And, voila! My new favorite pants for spring.