Apps won't update:
Turn your device off and back on. If this doesn't help, sign out from your account and sign back in.
Slow iPhone:
Try to reset your device. This won't delete your data stored on this device.
- Press and hold the Sleep/Wake button
- Press and hold on the Home button
- Keep holding both buttons until the display turns off and back on with Apple logo on it.
Alternatively, you may go to Settings - General - Reset - Reset All Settings
If this does not help, restore your device to factory settings. Note that this will erase the data from your device.
Take a look this Apple Support article: Use iTunes to restore your iPhone, iPad, or iPod to factory settings - Apple Support.
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