Paypal subscription

We currently use the paypal API to offer fixed button, one time purchases on a site.
We would prefer to have these one time purchases become subscriptions.

You will not have direct access to the site but the dev will give you everything you need and will work with you.
The job is to do the following.

-Change the buttons to dynamic prices so the prices can be changed as needed.
-Change our fixed buttons to subscriptions.
-Offer a way for users to cancel their subscription at any time on our site or they can do to paypal.