WhatsApp for Samsung I9190 Galaxy S4 mini

Long-press the home screen and remove every app shortcut except Phone, Contacts and Messages. To go further, disable the apps you can't uninstall via Settings > Application manager > swipe to the All tab > tap each app (Internet, Play Store, Email) > Disable. For an even cleaner setup, install a minimalist launcher like KISS or Olauncher from the Play Store first, set it as the default home (Settings > Application manager > pick your launcher as default), then disable the rest. See how others solved this on Reddit

The I9190 officially tops out at Android 4.4.2, so many newer Play Store apps will refuse to install. If you want a more usable device you can flash an unofficial LineageOS build for the S4 mini family via TWRP recovery (this wipes the phone and voids warranty, so back up first). Otherwise, embrace it as a calls-and-texts-only phone where the outdated OS no longer matters because you've stripped it down. See how others solved this on Reddit

Open Settings > More networks > Mobile networks and turn off Mobile data, and turn off Wi-Fi (Settings > Wi-Fi) when you don't need it, since background sync on Android 4.4 is a major drain. Then go to Settings > Application manager > All and disable Gmail and social apps you don't use. On a dumb-phone setup you can leave only the cellular radio active, which sharply cuts heat and standby drain. See how others solved this on Reddit

Open Settings > Application manager, swipe to the All tab, tap the stock Internet browser (and Chrome if it's installed) and choose Disable so they can't be launched. To fully cut the web, go to Settings > More networks > Mobile networks and turn off Mobile data, leaving only calls and SMS working. See how others solved this on Reddit

Back up contacts to your Google account first via Settings > Accounts > Google, then go to Settings > Backup and reset > Factory data reset > Reset device. If the phone won't boot normally, power off and hold Volume Up + Home + Power to enter recovery mode, use the volume keys to highlight 'wipe data/factory reset', and confirm with the power button. See how others solved this on Reddit

The I9190 has only 8GB of internal storage, so move photos and music to a microSD card via My Files > Device storage, long-press the files and choose Move > SD card. Then clear cached data through Settings > Storage > Cached data, and disable or uninstall bloatware under Settings > Application manager to reclaim the space those Samsung and Google apps take up. See how others solved this on Reddit