You can perm your hair any way you like depending on the texture and condition of your hair. Perming should not be done by people who are not professionals.  If the technique is wrong then chances are that your hair might end up being damaged.

Your curls may become a little relaxed after you shampoo your hair but it will never go away totally. It will gradually go once your hair starts growing. The new growth will be straight. You would need to perm the new hair appearing on the scalp. This can be done at an average interval of 4-5 months.

If you prefer a less curly look, then you can perm using large rods. Your stylist will guide you on this. Before perming, it is necessary for you to find out whether your skin has any scalp irritation or abrasion. Perming can take some time. So make sure you have at least a couple of hours in hand when you go for a perm. If you rush it, then you will be the loser. Perming requires the use of various chemicals which can damage the hair. So do not make it a habit.