Read this article and another and yet another before you upgrade to Windows 8/8.1 or Windows 10. Many people don’t like Microsoft’s new strategy based on removing features, adding telemetry and Windows 10 ads and replacing Aero Glass with primitive flat-looking Metro theme (you can restore Aero Glass transparency using glass8, but it’s unstable). If you still want to use it you can install ClassicShell. It restores start button and Windows 7-like start menu (you can also choose XP-like). It can bypass Metro screen on Windows 8/8.1 on start-up. There are a lot of new options in 4.0.0 including full support for Windows 8.1 RTM.
You can also install aero theme without transparency for Windows 8.1 or an old windows classic theme (install uxstyle first).