Iron on the inside, press on the outside using a cloth.

When ironing you move the iron acros the garment, when pressing you just press, and adjusting the pressure to the fabric composition is advisable.

I have regularly remade my kilts, and have learned to undo the stitching and then iron the fabric until it is flat, showing no remnant of the pressing of the previous incarnation, or the pleats will not lie down properly.

I then measure for the new size and put in safety pins top and bottom so I can fold the fabric and press the fold on what will be the inside face of the pleat before starting to sew.

If you work on the inside of the hem to first flatten the fabric - go slowly and use minimum heat, turn the dial up little by little so you reach the point where the heat will take out the folds without melting any man made fibre in the fabric.

Then fold the hem, press it lightly and sew it in place, and then press the folds once the sewing is done.

If you pin the hem don't iron or press over the pins or you will get a mark in the fabric.