to specify where Visual Studio search for the assemblies which you reference in your project

Unfortunately Visual Studio doesn't allow you to edit to reference assemblies, then you need to open the project file by a text editor and directly edit the ta and save the project file. When Visual studio detects the file change, it will ask you to reload the file.

Example:

<Reference Include="YourAssembly.dll">
<SpecificVersion>False</SpecificVersion>
<HintPath>C:\CommonAssemblies\YourAssembly.dll</HintPath>
</Reference>

to specify where Visual Studio search for the assemblies which you reference in your project