With Respect to .NET Framework 4.6 and Visual Studio 2017 you can take the below steps:
On the option bar at the top of visual studio, select the 4th option "Project" and under that click on the last option which says [ProjectName]Properties.Click on it & you shall see a new tab has been opened.Under that select the Application option on the left and you will see the .NET Framework version by the name "Target Framework".
Under Solution Explorer's tab select your project and press Alt + Enter.
OR simply Right-click on your project and click on the last option which says Properties.