Update 1.3.3 is only important if you have enabled international billing addresses for your checkout. Previous versions would “forget” the user’s chosen country if there was an error during checkout. That’s not happening anymore.
You should see the update option in your WordPress admin.
Author: Jason Coleman
Jason is co-founder of Paid Memberships Pro, the 100% open source membership plugin for WordPress. He has been pushing WordPress to its limits for many years and is an advocate for using WordPress as an application framework to build web sites and apps that go above and beyond the typical blog of CMS site.