Yes, you'll need to uninstall the RC before installing the final release. The final install should prompt you to do this if you haven't already.
You do no have to do anything to existing projects. However if you're planning using your projects with Team Build you'll need to add the import of Microsoft.WebApplication.targets to your project files.
<
Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" />
<Import Project="$(MSBuildExtensionsPath)\Microsoft\VisualStudio\v8.0\WebApplications\Microsoft.WebApplication.targets" />
This needs to be imported after the existing language .targets file. New WAP projects will have this by default.
Hope this helps,
Brad.