Hi,
I suggest to open a Support Ticket for your questions.
You can update IVR to the new version deploying the Fixlet #253 - Upgrade BigFix Retrieve v.4.1.1.0 that is available in the site BigFix Insights for Vulnerability Remediation
If you still have the IVR v.2.x you have to install IVR 4. there is no upgrade path from IVR v.2 to v.4, since they are different installations.