Hello,
Yes you can upgrade from RU6 MP3 to SEP 12.1
https://www-secure.symantec.com/connect/articles/upgrade-paths-sep-121amber
If you don't see it on fileconnect then as llower04 said, you will have to contact license department.
- They will check if a customer has a valid support contract.
- If he/she does have a valid contract then they will generate the notification email and send the same to the customer’s Email address.
- Once customer receives that, he/she just needs to go to the link mentioned in the Email and download the SEP 12.1
License department will ask you serial number which starts with M , Keep it handy before calling.
Customer care dept. confirmed that they are in a process of sending the Emails to all customers who has valid support contract in alphabetical order, however if one has not received then he/she needs to follow the procedure mentioned above