If you’re referring to this planned change, that’s related to PayPal’s SSL certificate, not the one you’re using on your server.
Basically, PayPal will be using a certificate that’s signed by a new root certificate. Some clients might have code that validates that their certificate is signed by the root certificate they’re currently using, or might have an outdated root store where the new root certificate isn’t included, and that would lead to breakage with this upcoming change.
Communication between PayPal and your server (i.e. when PayPal is connecting to your server) is not affected by this. If it’s working right now, it should continue to work regardless of this change.