WhatsApp for Samsung Galaxy S5 (octa-core)

Years of system updates and accumulated app cache bog down the older Exynos chip, so start by going to Settings > Application Manager, swiping to the Running tab and clearing cache on heavy apps, then disable bloatware you never use by tapping an app on the All tab and choosing Disable. For a real refresh, back up your photos and contacts and do a factory reset via Settings > Backup and reset > Factory data reset, which clears the gunk that builds up over the phone's life. See how others solved this on Reddit

Like the long-lived older Samsungs people keep using, the S5 stays usable if you swap in a fresh battery (it has a removable back, so a new OEM cell is a five-minute fix) and keep storage from filling up. Move photos to a microSD card and uninstall apps that have outgrown the hardware, since modern social apps are the main thing that makes a 2014 phone feel sluggish. You can check space and free up storage under Settings > Storage. See how others solved this on Reddit

The S5 can run Pokemon GO but the older Exynos GPU and limited RAM cause stutter, so lower in-game graphics, enable Battery Saver inside the game's settings, and close background apps from the recent-apps button before playing. Make sure Google Play Services and the game are updated through the Play Store, and set location to High accuracy via Settings > Location > Locating method to avoid GPS drift that breaks gameplay. See how others solved this on Reddit

The octa-core S5 (Exynos, model G900H) officially tops out at Android 6.0.1 Marshmallow, so if Settings > About device > Software update shows nothing new, that is expected, not a fault. To get newer features you would need a custom ROM like LineageOS, which requires unlocking the bootloader and flashing via TWRP, though for a daily phone it is safer to keep the stock build patched and your apps updated from the Play Store. See how others solved this on Reddit

Back up your S5 first by enabling Google account sync under Settings > Accounts > Google (contacts, calendar, app data) and Google Photos for pictures, then on the new phone sign into the same Google account during setup to pull it all back. For Samsung-specific items like messages and settings, install Samsung Smart Switch on both devices and transfer wirelessly or via a USB cable, which carries over far more than the basic Google sync. See how others solved this on Reddit

For light use like calls, messaging and the camera the S5 still holds up, and a cheap new battery plus a factory reset can buy it another year. But it no longer gets security patches and many banking and chat apps now drop support for Android 6, so if those apps start refusing to install or log in, that is the signal it is time to upgrade rather than fight the hardware. See how others solved this on Reddit