After switching the mobo, you will probably need to reinstall Windows (sometimes you won't - but I have never been that lucky).
Before you switch mobos - do the following:
1) Visit Gigabyte's website and download all of their current drivers for Windows 8.1 to a flash drive (or make a DVD). Most of the time Windows will get you to a point that you can download the drivers....but better to be safe that sorry.
2) While on Gigabyte's site, download the latest BIOS updates to a flash drive - again, you may need it and it is better to be safe than sorry.
3) Make sure you have your Windows DVD/bootable flash drive ready and your product key ready.