First of all, make sure that you baby meets the proper weight and age requirements for the carrier. Check your carrier to make sure that the leg hole surrounds the baby's leg entirely even when seat is adjustable.
Machine wash gentle cycle and line dry or tumble-dry on lowest setting.
Allow to cool before using. Only certain carriers are designed for use as a back pack type carrier. Some do contain a waist belt, however it is only a matter of personal preference. Walmart, Kmart, Toys R US, Babies R Us, Burlington Baby Depot, USA Baby and other specialty stores nationwide. 6 months up to 40 or 45 lbs depending on the model.