When 5 or 7.5 cm (2 or 3 inches) of the fabric at the bottom of a curtain lays flat on the floor, the effect is called "puddling." This is an elegant effect in a formal room, but it is not appropriate for a casual room. It is also a poor choice for curtains which are opened and closed frequently. If your curtains puddle too much, you may shorten them up to 30 cm (1 foot) without cutting the fabric. Turn up an extra hem to get your curtains out of the way.
Use a seam ripper to remove the hem from the curtains. A seam ripper is a sharp hook with a handle that you insert into a seam to cut the threads. It is available in the sewing notions section of a fabric shops. You do not need to take the curtains down to let down the hem.
Determine how much you need to shorten your curtains. Fold the bottom edge of the curtain back at floor level and measure the distance from this fold to the bottom edge of the fabric. Divide this number in half.
Take down the curtains and iron up a hem in the bottom edge equal to the distance you calculated. Fold the hem up again the same amount. Pin this hem in place.
Hemstitch the top of the first fold to the curtain. Thread your needle and knot the thread. Start at one end of the hem. Run your needle through the edge of the fold. Use your needle to pick up two or three threads in the curtain fabric just behind the fold.
Take another stitch through the edge of the fold 6 mm (1/4 inch) further along the hem. Continue along the hem alternating stitches in the fabric with stitches through the fold until the entire hem is sewn in place. Rehang the curtains.
If you are hanging the curtain for the first time, hang the curtains with the pinned-up hem for two weeks to allow the fabric to stretch. Then sew in the hem.