What does "system restore" allow users to do?

System restore allows users to revert the operating system to a previous state, making it a valuable tool for troubleshooting problems that may have arisen due to recent changes, such as software installations or updates. This functionality works by using restore points that capture the system’s state at specific times. Using system restore can help resolve issues without affecting personal files, such as documents, photos, or emails, thus providing a safer alternative to options that might result in data loss.

The other options represent different functionalities; upgrading the operating system refers to changing it to a newer version, resetting the computer to factory settings erases all data and applications, and backing up files involves saving them externally but does not relate to restoring the operating system's functionality.