The full process for upgrading to 14.2 is here:
https://www.symantec.com/docs/TECH247759
However, be aware of the known issues in 14.2 first to ensure they won't affect your environment. Listed here:
https://www.symantec.com/docs/TECH250794
https://www.symantec.com/docs/TECH250508
https://www.symantec.com/docs/TECH177101
https://www.symantec.com/docs/TECH250749
https://www.symantec.com/docs/TECH250946
https://www.symantec.com/docs/TECH250796
https://www.symantec.com/docs/TECH250795
If you think they won't affect you then feel free to upgrade. Backup first, obviously.