The process of reinstalling an older version of the iPhone operating system, rather than the currently installed one, is a procedure some users may wish to undertake. This action typically involves downloading the specific iOS firmware file (.ipsw) desired and utilizing a computer to initiate the installation through iTunes or Finder, depending on the operating system.
There are instances where returning to a prior iOS release might be necessary. For example, an updated version could introduce bugs or performance issues that negatively impact device usability. A return to a more stable release could resolve these issues. Historically, this ability has allowed users to circumvent software-related problems until Apple addresses them with subsequent updates.