(photo credit, Google)
The first thing I did was to lay the pant legs flat out on a table, pulling the outside seam taut and flat. It is okay if the inseam is a little bunched up. You will only be altering the outside seam.
Mark 3/4 inch measurement with pin. Gradually taper/pin your measurements to form the pantleg. This might take some adjustments, so keep trying until you have a proper increase toward the hem. This requires a bit of precision. You might even want to measure your calf to determine the width of the finished pantleg. Be patient, or you will end up with a really funky pair of pants.
Next, cut along the outside of the pins. Make sure to cut the fabric and keep it in one piece. When you have trimmed the pantleg down, it will look like this:
Next, take the piece of fabric that you trimmed off of the first pantleg, and line it up along the taut, flat edge of the second pantleg.
Using the excess fabric as a template, pin and trim just as before.
When both sides are pinned, sew along the INSIDE of the row of pins, gradually tapering the pantleg.
Remove pins, trim down the seam to about 1/2 inch, and turn pants right side out. Viola! Refashioned leggings!