Hi Supercell29,
Upgrade process is very simple but first learn what new in SEP 12.1 Eg. License concept, SONAR, Download Protection etc..
I would like to suggest following plan
1) Learn what's new in SEP 12.1
2) Take a backup of existing SEPM
3) Proceed with upgrade
Step 1.
Check following article for more info.
What's new in version 12.1
http://www.symantec.com/docs/HOWTO55189
What is new in Symantec Endpoint Protection 12.1
http://www.symantec.com/docs/TECH163413
Step 2.
Prior to upgrade take a backup of existing SEPM
http://www.symantec.com/docs/TECH102333
Make sure you have sufficient disk space.
The SEP 12.1 SEPM upgrade installer requires three times the current database size (sem5.db) if upgrading from pre-12.1 SEPM with the embedded database only.
Reference : http://www.symantec.com/docs/TECH162730
Step 3.
Start upgrade process to learn more about upgrade go through following article
http://bit.ly/sDogRu
I hope it will answer your question.