First check the PAM entry for the supporting OS and DB to upgrade the system to NetWeaver 7.4
The upgrade guide contains a substantial amount of information
You can use the SAP Solution Browser tool which is now known as the SAP Innovation Discovery to know what comes with the NetWeaver 7.4 version.
SAP Service Marketplace - SAP Improvements & Innovations
The best thing is to do a system copy of the production system to the sandbox and upgrade the sandbox to the target level and finally test the system. This will let you identify the potential impact and benefits of upgrading the system.
Additionally read these SAP notes
1730102 - Release Restrictions for SAP NetWeaver 7.4
1751237 - Add. info about the update/upgrade to SAP NetWeaver 7.4 (incl. SPs and SRs)
Cheers
RB