.NET versions are often installed as 'programs' so appear in the Programs and Features list, rather than in the Installed Updates list (it depends on how your installed them)
Windows 7 comes with versions 2, 3.0 and 3.5 installed (in effect - all you'd see would be v3.5)
v4 is quite possibly irrelevant to anything you're using - except possibly your graphics card drivers
v4.5 is almost certainly irrelevant.
Note that the versioning in .NET doesn't follow the usual rules, - it's possible to have the following versions of .NET all installed at the same time, since they do certain things differently (or not at all)
v1.0 or 1.1
v2.0 (and SP levels)
v3.0 or v3.5 (and SP levels)
v4.0 or v4.5 (I'm not sure about the equivalence here)
I just wish that MS would release a catch-all that had a decent cleanup for earlier versions!