(EDITED on December 9, 2020). As you probably already know CentOS 6 is reaching its End Of Life in November of this year. So if you still have a distribution of CentOS 6 it’s high time to upgrade.
Our advise is to probably stick with v7 (which will be EOL in June 2024). Since the EOL for the "regular" CentOS Linux version 8 has just been changed to "the end of 2021" (read this announcement from CentOS). If you are currently on V8, check out the possibilities you have for upgrading CentOS 8 to CentOS Stream 8.
Depending on what you are running on the v6 the easiest way to upgrade is to have a second server with a fresh install of CentOS 7 and migrate everything from 6 to 7. This way you can test your new environment safely and if anything goes wrong, you still have your v6 up and running.
If you have a Tilaa Managed Server Pack, please contact support if we have not already contacted you about the EOL for CentOS 6.
More information can be found in the CentOS Migration Guide
If you have any questions regarding the update/migration/EOL or if you want additional information, you can always open a ticket with support.