I have a new install of SQL Server 2014 at 12.0.2000.8 and I want to upgrade it to 12.0.4213.0 as this is the version the production server is running at. How do I do this? Thanks!
Check out this site for SQL Build Numbers. It is a comprehensive list of build numbers for SQL Server. https://sqlserverbuilds.blogspot.ca/#sql2014
According to this list of build numbers, you will first have to apply Service Pack 1 for SQL Server 2014 which will bring you to 2014.120.4100.1. Then you will have to apply MS15-058 which will bring you to 2014.120.4213.0 as requested.
The blog post will have links to download the service pack and patch. Obviously, with any upgrade, please take care. Make sure you have proper backups of your databases before hand. If a VM, taking a VM snapshot before the upgrade is a good idea. While I do not expect you to have issues running these installs, it is best to always have a backup ahead of time.
Additionally, please make sure you read the documentation pertaining to each of these updates so you can be fully aware of what they will do to your environment.