Is it necessary to update/install Microsoft .NET Framework 4.5?
Only if an application requires that version. It isn't required for Windows itself.
Latest AMD drivers ( there are two versions, one version requiring dotNET 2.0 ) for graphic cards 5xxx, 6xxx, and 7xxx require dotNET 4.0 to be installed for CCC operation. dotNET 4.5, I believe, is an advanced version of dotNET 4.0. You may install it to make your computer future-proof. CoolGuy