Paypal and Authorize.net have officially announced that they are disallowing the communication via SSL 3.0 and are notifying the customers. So many store owners having Paypal and Authorize.net as their payment processors have started questioning what they should do.
In short, you don't have to do anything. All payment plugins of J2Store that use cURL to communicate with payment processors like Paypal and Authorize.net DO NOT have an SSL version specified. That means they use auto-negotiation of SSL version.
PHP 5 and lib curl can actually auto-negotiate the best level to use as long as no SSL version is specified. So when a cURL request is made, PHP auto detects the best security level and uses it. Since Paypal and Authorize.Net disable SSL v3 support, the curl library will auto-negotiate to TLS.
So all the J2Store payment plugins including Paypal and Authorize.Net should work WITHOUT any issues.