In Response To 'Re: Stylesheets'
In reverse order,
If stylesheets are installed where they are supposed to be (under $UserBaseDirectory or $BaseDirectory, in the subdirectory SystemFiles/FrontEnd/StyleSheets/ ) they will survive Mathematica upgrades.
File menu - Install - StyleSheet handles this automatically.
Main question: if you have used Format menu - Edit Stylesheet to create or modify a style, you can save the style sheet with File menu - SaveAs, OR just click the InstallStylesheet button in the upper-right corner of the "Private Style Definitions" window.