[visual-studio-2010] Converting VS2012 Solution to VS2010

the simplest solution is.....open your website in vs2013 and go to Debug->WebsiteProperties (last option) a new window will open..

in this window go to "Build" option and change .net framework version from 4.5 to 4.0.....then select ok. [note: this step will only work if your project does not have dependencies with vs2013...]

Now open your website in vs2010