Updated: February 24, 2020
What's the Latest Version of iOS for iPhones and iPads? - At the moment the most latest version for iPhone and iPads is OS 13.3.1
To check for iOS updates for this device, go to the menu "Settings → General", select "Software Update" and wait for the data to load.
How to install latest version of iOS on iPhone and iPad: Just go to the section "Settings → Basic → Software Update" mentioned above and click the "Download and install" button. All available data will be saved on the device. It is important to remember that installing iOS "over the air" in any case can not be carried out if there is a jailbreak on the device.
Can I install not latest version of iOS? - No. Apple does not allow you to install outdated versions of the operating system on your mobile devices (i.e., roll back or downgrade the iOS version), so only the latest firmware released for each gadget will be available.