A couple of things you need to keep in mind. The internal storage in your Tab 4 is divided into several different partitions, most are dedicated to the operating system and one is set aside for the user, a data partition. That's where all all your data, your settings and config files, and anything else relative to your login account get stored. A Factory Reset only wipes that data partition, this clears all the user data and it does NOT do anything all at to any of those operating system partitions. The OS is left as is, it's just the user data that gets cleared away. To replace the installed operating system, you need to 'flash' your Tab with its appropriate ROM. Flashing the ROM is essentially the same as using a Restore disc/image to replace the OS on a computer. The installed OS gets replaced with a 'clean' OS. So depending on why you want to 'reimage' your Tab, you've got those two options. Factory Reset or flashing the ROM.
If you do opt to flash your Tab, go here to download the appropriate ROM:
https://updato.com/firmware-archive-select-model?q=sm-t530nu&exact=1
Updato is a good source of to get verified, stock, Samsung ROMs so there's a lot less chance of a problem than downloading a ROM from some anonymous web site. Be sure to pick the ROM that exactly matches your Tab and your carrier. ROMs are not interchangeable with each other and it's important to only use the correct one. Different models have different internal hardware configurations, and it's matching ROM needs to have the corresponding software (firmware, drivers, apps) that work with that specific hardware.
For a detailed, step-by-step instructions on how to do the flashing process, go here:
https://updato.com/how-to/how-to-install-an-official-samsung-stock-firmware-using-odin
But before you start to do this, be sure you've got all your saved data safely backed up. You might find Samsung's Smart Switch utility handy to do a full backup and restore.
https://www.samsung.com/us/smart-switch/
Using the Odin utility correctly, your saved data should be left intact but backing up is still necessary in case you run into a glitchy problem. Flashing the ROM is an involved process regardless. (and backups should be done regularly anyway).
One other point on the Odin utility, it was for a time not very backwards compatible so working with older hardware might pop up an error message or just fail. So if you do encounter an issue you should try using an older version of Odin. You can download multiple versions from here
https://www.droidviews.com/download-odin-tool-for-samsung-galaxy-devices-all-versions/
and pick the appropriate one that corresponds with your particular situation.
Also, if you don't have easy access to a Windows PC (Odin is a Windows utility), there's an Open Source alternative called, Heimdall. It's not an exact duplicate (some menus are in different locations with altered naming but it is similar in functionality) but it's available for Linux, OS X, and Windows.
https://glassechidna.com.au/heimdall/
