This is a pair of shorts that I resized, once a 14, now my size. Just a pair of shorts from a thrift store.
I took them in on the sides and center back seam, ripping the waistband enough to take it in from the inside, and then top stitching it in place. This is a little tricky, trying to turn it around enough to keep the taking-in even and strait - but it's doable, anyway.
There's a couple of options to where you can take them in - the sides are the simplest place, which is good if you have a pair of pants that are just a couple of inches too big. The biggest problem with this is that if you take them in too much, you'll make the pockets too tight for your hands.
This isn't so good (trust me, I've done it more than once!), so if you need to take it in more, you can slide the back out so that there is a bigger seam allowance in the back than in the front, which you can use to control how much you want to take in without taking too much from the pockets.
Or, you can take in the back seam too. You have to make sure that the new seam has a nice, smooth curve down to the inseam, meeting the old seam before you reach the inseam.
Since my shorts were so much bigger, and I like big pockets, I had to do both the slidy thing a lot and the back seam thing a lot - the end result is shorts that are kinda baggy with wide legs, which I think I like better than if they had been my size to begin with!
The jumper is from the thrift store too, a vintage lambswool sweater for a dollar - It's like my favorite sweater.