I hacked-installed 8.1 update and do NOT recommend it. I of course also did the 'upgrade' from windows 7 install.. Everything got botched from 8 - 8.1, BSOD's left and right. specifically kernel_data_inpage_error, but also critical_process_died, and sometimes hex codes. All over the map with 20 min uptime before crashing. The problem was bad drivers and the fix was updated drivers... Due to it being sloppy and my drive 90% full I did a complete reinstall, and heres how.
1) backup everything important. export bookmarks, emails, configuration/setting files, take screenshots of confusing network shares, etc. You'll be starting fresh.
2 - optional) Refresh your PC without affecting your files. This will basically work like reinstalling windows over itself, except more intelligent as it will hash the install files to your HDD files and overwrite those which don't match - like 4 min on my SSD. The key is it generates a list of what was installed before wiping it. Once complete, log back in and copy the HTML list it generated of your now uninstalled programs to a USB/network share/DVD or whatever. this seemed quicker than any other method I could find to know what I should reinstall. It left a bunch of crap all over the C drive, so I carried on.
3) remove everything and reinstall windows. Pretty self-explainatory. It will ensure windows 8.1 is how it should be. it cleaned up my C: folder and booted into a 'from factory' boot when you first get windows 8. If this step or optional 2 says your missing files you need to pop in the full install, but upgraders should find the install.wim on the install/update media you hopefully made (USB/CD/ISO) and copy it to c:\refreshimage and then use command prompt to set the image so windows can refresh and restore from it. Google should help.
4) reinstall Windows 8 updated drivers for your devices. You can leave the MS ones there, but you only get basic functionality. ensure device manager has no question marks or exclaimation points. I had to go to properties and hardware ID and search the line on google to find the correct drivers for some. I was using windows 7 packages thinking they were 'good enough', was I wrong.
5) I'd suggest making a restore image at this point so you can always start here again.