An object-oriented and type-safe programming language that has its roots in the C family of languages and includes support for component-oriented programming.
in the new project style, which supports building multiple framework versions, the build is always under the framework folder name. nuget package references are in the project rather than a separate file (packages.config)
there is no downgrade tool. the easiest is to create a new class lib with the version you want. add in the nuget packages, and the source code.
note: the extended support of vs2013 ends 4/9/24. net 4.* < 4.8 support has already ended. for security reasons you should upgrade to 4.8