An admin can update FlexForm anyway he prefers.
If the FlexForm extension has its own git initialized, then FlexForm's Special Page might make updating even easier.
FlexForm's special page is only accessible for a sysop and it will show FlexForm's current installed version and if there are any updates available.
Also a changelog will be shown to quickly check what the new version(s) has to offer.
If you have FlexForm's installation connected to Git, then you can click the button on the Special page to have FlexForm git-checkout the latest version.
Any messages and feedback will be shown on the page itself.