In Microsoft Visual Studio 2010 VC++ directories are no longer a property of the IDE, so it is not possible to modify them from Tools->Options->Projects and Solutions->VC++Directories, it is necesary to specify them as project properties.
However, those who installed VS2010 on a box where a previous version was already installed, will find the same predefined directories. This is an annoying problem if those directories are outdated: suppose you install a newer version of some libraries (e.g. boost): then you need to remove the older one, but how?
Here’s the solution: go to $(USERPROFILE)\appdata\local\microsoft\msbuild\v4.0 and edit the profile files there (Microsoft.Cpp.Win32.user.props, in most cases).