Hi,
Thank you for posting in Symantec community.
From SEP 12.1 RU1 onwards Symantec is giving an options to download full product in two parts i.e par1 & part 2 or download individual files like SEPM setup, SEP 32 bit setup, SEP 64 bit setup, Tools as per the requirements.
It gives more levarage to the Symantec customers to choose what he wants. In many cases it's seen that customers used to required only SEP setup and unnecssarily he had to download entire zip file which was around 1.5 GB in size.
Either extract Part1_Installation_EN or SEPM_EN.
You will see SEPM folder and it includes setup.exe.
Release Notes and System Requirements for all versions of Symantec Endpoint Protection and Symantec Network Access Control
http://www.symantec.com/docs/TECH163829
There is not any major change in the upgrade process. Only change is Port 8446 will be used for Remote Management web services.
Upgrade process from SEP 12.1 RU1 MP1 to SEP 12.1 RU2
https://www-secure.symantec.com/connect/articles/upgrade-process-sep-121-ru1-mp1-sep-121-ru2