I had this pair of cool looking pajama pants that I got from Aeropostale but they shrank awkwardly and looked weird as pajama pants. I suddenly got the idea that I should change them into a pair of skinny jeans since they are a thick-ish flannel material. This honestly only requires two lines of stitching to slim them down. That's it. I like how they're a little more breathable than regular skinny jeans.
It really helps if you have an pair of skinny jeans to lay out and replicate, or general knowledge of skinny jeans.
Look at the pajama pants. Figure out whether it's the outer seam or the inner seam that has the "fancy seam"- generally meaning that it's folded over and sewn over. YOU DON'T want to sew on the side of the pants that has that seam because it looks better. YOU WANT to sew on the side of the pants where the seam is just plain on the leg.
Make sure you do EITHER the red seams or the purple ones depending on where your "fancy seam" is. MAKE SURE that the first time you sew the seams that you don't do a tiny stitch or use an overlock machine because you want to make sure that they fit before you do the "final draft seam" which will be smaller.
You can just use and pair of skinny jeans to map out where you want your seams.
This is what mine looked like after I tried them on and only sewed one leg with a rough stitch.
Once your final stitching is complete, overlock outside the seams or you can trim the excess fabric off and zig zag stitch the seams.
If you have any questions or this is too confusing, ask, or there might be more informative tutorials about changing jeans to skinny jeans that can be used in this same situation. Thank you for your time!