PayPal Security notice, do I need to take action / upgrade Civi?
It seems it is about your ssl connection, so it's on the openssl layer connected to your webserver (apache or nginx).

Test your ssl connection with that site, https://www.ssllabs.com/ssltest/ it will tell you what needs to be improved.

In short, nothing to do with civicrm, but upgrading to the latest version is always a good idea anyway