With the release of SSDT RTW, it is no longer required to remove previous installations of SSDT before upgrading to a newer release.
This means that if you have CTP4 or CTP4 Update 1 on your machine and you wish to upgrade to RTW, you can install RTW directly without uninstalling your existing verion of SSDT or its dependencies. Please note that in-place upgrade from CTP3 to RTW is not supported. Instructions on uninstalling CTP3 are detailed in this blog post.
If you run into any installations issues or have a question, please let us know on our team form: http://social.msdn.microsoft.com/Forums/en-US/ssdt/threads