I'm Greg, an installation specialist, 9 year Windows MVP and Independent Advisor, here to help you.
You can opt out of the Insider Program in Settings > Update & Security > Windows Insider Program. Then see if you can still Go back to the last stable version at Settings > Update & Security > Recovery.
if not you can wait for the next stable version and run it as an Upgrade by installing the Media Creation Tool from this link choosing Download Tool Now, install the tool, open it and choose Upgrade this PC Now. http://windows.microsoft.com/en-us/windows-10/m.... This will save your files and apps while bringing you up to the latest version by the most stable method. It will also bring all of your Updates current and solve most problems since it reinstalls Windows.
Or you can Clean Install following the illustrated steps in this link which include everything that works best in Windows 10: http://answers.microsoft.com/en-us/windows/wiki...
Your files should always be backed up because a hard drive can die at any time without notice. Some suggestions to help ease into this habit:
You can sync your Desktop, Documents and Pictures folder in Onedrive using Folder protection, or just drag valuable files into OneDrive folder, offering 5gb free with additional space for cheap: https://www.tenforums.com/tutorials/116029-turn...
Google Drive has a new Backup that allows you to choose User folders (Documents, Pictures, etc.) to sync up to 15g for free to their cloud in real time so it always has the latest version. https://www.google.com/intl/en-GB_ALL/drive/dow...
Or you can manually drag or copy them to another hard drive, USB external or flash drive. Here's how to drag, copy or move large groups of files: https://www.pcworld.com/article/2086566/the-man...
Besides your files you should back up a System Image to use in place of reinstall in 20 minutes. The best free alternative is Macrium: http://www.howtogeek.com/howto/7363/macrium-ref... You can even use the Macrium program to mount and extract files from this image so it can serve as both image and file backup too.
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.
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