I have been told that .Net Framework 4.5 is the in place update of version 4. And So does happen for the .Net Framework 4.5.1. And actually the necessary dll of .net framework will be replaced when been upgraded. So my question is can I compile a project which target framework is 4.0 in 4.5 environment installed system?
Yes, you can.
The only breaking change I've encountered so far is in debugging - the debugger interfaces changed in 4.5, which can be tricky if you're trying to debug process dumps. It's not an issue if you use the latest Visual Studio (or just use WinDbg, although that certainly isn't for everyone) and copy the framework directory from the computer that had the error, but it's very annoying.