Changing your billing plan on Page An Engineer is simple and easy to do. First you need to make sure that there is an active payment method attached to your account. Following attaching a payment method you go to this link and scroll down to the billing section in which you can use the drop down to select a plan that is different than your current one.
You can find the details of what each plan includes on the pricing page found here. A great way to save money is to sign up for an annual plan which reduces your total yearly bill by up to 2 months free.