Jeans? You cannot. Give up on those jeans and/or wear a good belt.
From, Someone who has only ever lost weight, and owns jeans in 3 different sizes (and remains in denial thus still hasn't bought a fourth size—but used some undershorts for summer and got some good belts; and doesn't care about a flat-looking butt.)
Do you have a sewing machine? You could sew along the inner seam (like the part between the legs) to make them smaller. I've made skinny jeans that way and they look OK. It doesn't do anything to the waist though :)