How to uninstall the software and reinstall the latest software in iPhone?

If you are referring to an app, delete the app and then reinstall it on the App Store. The App Store will automatically install the latest version of the app. If you are referring to IOS, you can't really uninstall IOS. You can, however, preform a factory reset, which will completely wipe your iPhone, including all data and settings, and install the latest version of IOS.

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Jonasilver137

If you want to install a clean version of iOS, you would want to use your computer with iTunes (Windows) or Finder (Mac). Backup your iPhone to your computer, then restore the backup to your iPhone and in the process, iOS will download the newest version as part of the restore process.

See how to do that in this link --> Restore all content to iPhone from a backup - Apple Support (AM)

See the last section on restoring from a backup. Make sure the backup is the one you made on your computer, before you do the restore.