There are usually two places to add length to a pattern:  If you have a longer torso than is normal, you would add up to an inch above the waistline.  Split the pattern (on the indicated line if there is one) horizontally about 2-3" above the waistline.  Then spread the pieces apart the desired amount and tape paper under the opening.  To make the hem lower, add length to the bottom, following the shape of the hem.  Allow enough width at the sides to accomodate your hips with 2-4" ease space.  Alternatively, you can split the pattern below the waistline to add length as long as there is enough width for your hips.