Upgrading from level 0 to level 1 through paypal buttons

I am new to s2Member and am using the lite version.

I found a tutorial online that allowed generation of a button to upgrade or downgrade membership levels called the “Subscription Modification Button”, but now it has deprecated. Is there any way to replicate this functionality?

Not with the current PayPal buttons integration, sorry. PayPal removed the power to do that. https://developer.paypal.com/docs/paypal-payments-standard/integration-guide/Appx-websitestandard-htmlvariables/#deprecated-variables

You don’t need a modify button from Level 0, though… Level 0 is free, so it won’t be sold with a PayPal subscription. A free member at Level 0 can be sold the Level 1 with the button you have available without any problems. Did you try it and have any difficulty with it?