You can change how much you charge per minute by going into your account, and in Settings -> Calls add the desired amount you wish to get paid per minute. (1)

You can also have preferential prices for some customers, by just adding their Skype ID and the desired price you wish to charge them. (2)

Check the picture below to better understand where to find it in your account. You can also click the picture to be taken into your account's settings.