It just means you need to upgrade your SQL Server version before you upgrade K2.  You don't need a fresh install.

Hi David,
Thanks for your replay. If we upgrade SQL server 2012 to 2016 will it be impact any existing K2 Database ? After Upgradation to SQL Server 2016 ,I can do my K2 4.7 to K2 five upgradation right? 

We're also on SQL Server 2012. We upgraded to K2 Five without upgrading to 2016. Although it's not supported, it's also not blocked by installer. We talked to a K2 consultant who told us we should upgrade before running fix packs but he wasn't sure what the consequences would be if we decided it run them anyway.

I don't think it's recommended, but it does work.

Hi

Only K2 version 4.7 can be upgraded to K2 Five. Any previous version must first be upgraded to 4.7 before you can upgrade to K2 Five.

If there are any Database Triggers defined for K2 tables in the K2 Database, ensure that the triggers are disabled when performing upgrades. If they are not disabled during the upgrade process, errors will be reported by the K2 Setup Manager.After upgrading to k2 Five, you can now upgrade your database. Please click Here for more information.

Regards

Elvis

Good day Nik86

If you look at the support matrix and see that software is not supported that does not mean that your k2 version supports the software version but rather than the 3rd party software did not have a full testing lifecycle against the lited k2 version. We have a rule of thumb that if the support matrix indicates it is not supported, we see the software as unsupported.
To solve your problem/answer your question: Upgrade your SQL Server first to the latest supported version of the K2 version you want to upgrade to. This should not impact any database data. Then upgrade your K2 to the desired version. Please see the links below on how to upgrade K2 and SQL Server.

Doccuments:
K2 Upgrade: http://help.k2.com/onlinehelp/K2Five/icg/5.2/Default.htm#Install/UpdateManager.htm

Sql Server Upgrade:
https://knowledge.autodesk.com/support/vault-products/troubleshooting/caas/CloudHelp/cloudhelp/2019/ENU/Vault-Install/files/GUID-D17881EB-0D1D-45*personal details removed*C0-2F8F671AF94A-htm.html

Note: First perform these actions on your development environment and make sure you have a solution package(.kspx package) as a backup and a .bak file of your database as a backup.

Kind Regards
jacques.