My iPhone 4S performance is very very slow

Can you please be more specific? Realize your phone is pretty old. I have a 4S too and it is slow. That is natural as newer software and features require more powerful computing devices.

Try the following in order: (Note: If any step resolves the issue, STOP, do not go on to the next step.)

• Restart your iOS device: To restart your (perform a soft reset) iOS device, press and hold the sleep/wake button while pressing and holding the Home button. When you see the Apple logo, release both buttons. (Note: This will NOT delete any data or apps, nor change any of its settings.)
• Remove, and then, re-install the SIM card.
• Reset your iOS device's Wi-Fi settings: Settings > General > Reset > Reset Network Settings
• Perform a "Reset All Settings" reset: Settings > General > Reset > Reset All Settings
• Reset your iOS device to its factory default settings: Settings > General > Reset > Erase All Content and Settings
• Restore you iOS device: To restore your iOS device, connect it to your computer. When the iOS device appears in the iTunes source list, click the Restore button on the Summary tab. Note: This will erase all of your data and media and resets all of the iOS device's settings. You will need to restore it from a previous backup from either iTunes or iCloud.
• Make aGenius Bar appointmentat your local Apple Store or take it to anApple Authorized Service Provider.