If you don’t want your users redirected to your home page, you can open the file /wp-content/plugins/s2member/src/includes/templates/buttons/paypal-checkout-button.php and edit line 19 replacing
<input type="hidden" name="cancel_return" value="%%cancel_return%%" />
with
<input type="hidden" name="cancel_return" value="https://yourwebsite.com/desiredpage" />
It worked perfectly here and solved an annoying problem where users were sent to my homepage instead of the page where they can subscribe/upgrade.
I hope you find the information useful.
