You cannot 'shift' weight from your legs to your upper body. If you want to get slimmer legs then plenty of movement in the saggital plane i.e. felxion and extension at the hips and knee joints. Running, squats, lunges, steps, leg curls and leg extensions are all examples of this.

As for building your upper body, by doing strength training you will adapt to the stresses of your workload by what is called "hypertrophy" which is increasing of muscle fibres/cross section and stimmulation of these.