Samsung
Factory Reset: Settings Guide auf Samsung
A factory reset erases the internal storage of your Samsung phone and restores it to the state it had when it left the factory. This is the fix technicians reach for when a device runs slow after months of use, gets stuck in a boot loop, or needs to be prepared for resale or trade-in.
Before you start, back up photos, messages, and app data through Samsung Cloud or Google. The reset removes every installed app, every account signed into the phone, and all files stored in the internal memory. Content on an external SD card is not affected, but internal storage cannot be restored afterward without a backup.
To reset your phone, go to Tap on Settings ➔ Tap on General management ➔ Tap on Reset ➔ Tap on Factory data reset ➔ Tap on Reset ➔ Tap on Delete all.
After confirming, the phone reboots and starts the initial setup screen. Samsung devices ask for the previously used Google account credentials during setup as a theft-protection measure, so keep those details ready.
If the phone only feels sluggish, check storage usage or clear app caches first. A factory reset should be the last step once simpler fixes have not solved the problem.