Below are steps to make Magento upgraded website live.
Step 1: Setup clone database of the live database on the live server.
Step 2: Put live website in maintenance mode.
Step 3: Move all root directories and files of the live website to any subfolder. E.g. Create “old_live_site” folder on the root directory of the live website and move all folders and files of the live website to this folder.
Step 4: Copy all folders of the upgraded website and past to live website root directory.
Step 5: Point upgraded website folder to live database and run live website after removing maintenance mode.
Step 6: That’s it. If everything will be ok then live website upgraded with the latest database.
If you will face any issue then we can run old live website from backup using step 1 (Old database of live site) and step 2 (Old directories of live site)