Upgrading Netbackup 7.1

Hello,

Actually we are running Netbackup 7.1 on a single server running Windows Server 2003 (just for information, we do not have Netbackup support) and we want to upgrade to a newer version 7.6.

My question is, should we buy a licence or we can get it when renewing Netbackup Client Support?

My second question, can we make the upgrade on Windows Server 2003 or we have to upgrade the OS too to Windows Server 2008 or earlier versions?

Thanks in advance, and best regards to you all.