Windows Restore; Creating & Using a Restore Point
This may or may not come as a surprise to you, but Windows (or any operating system for that matter) is not perfect, or infallible. Just because you've created a system restore point, does not mean that you are guaranteed to be able to restore your machine to your old settings and regain access to you files! You
should be able to, but unfortunately, System Restore doesn't always work, for one reason or another. Also, it only stores you System settings, NOT your personal files.
If, when you're updating or reinstalling, Windows crashes and causes a system or file error that causes a system disk or partition error, you
could lose access to all of your personal files, so backup
before doing so! Where all of your personal files are kept is another thing to take into account. Windows stores all of your files in C:/Users/UserID, but it is safer to separate this off; see
Windows System if you're interested in how to do this.
Before you start on any update or reinstall, you should also ensure that you have a reinstallation disk and license key for your specific Operating System & Version (Windows/iOS/other, version no. [7/8.1/10, etc.] and specific Edition [home/pro. etc.] and type [32/64bit]), just in case the worst happens -