In VS2013 this isn't settable within VS itself.

To view the target framework

Project Properties > Common Properties

Ifa target framework is set (not all applications need it) then it is displayed above the right side main box(es).

To set / change a target framework

Close the project.

Open the projects .vcxproj with notepad.  Find the "<PropertyGroup Label="Globals">" section:

  <PropertyGroup Label="Globals">
    <ProjectGuid>{DF740E12-4588-4559-9BC6-761AF5F99AA4}</ProjectGuid>
    <RootNamespace>Hycal_PC_Software</RootNamespace>
    <Keyword>ManagedCProj</Keyword>
    <TargetFrameworkVersion>v4.0</TargetFrameworkVersion>
  </PropertyGroup>

If not <TargetFrameworkVersion> entry is found then you can add it here, and if it is then change the value here.  Close the file, re-open the project and verify the new framework version is shown in Project Properties.