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To address this issue, I would suggest restarting and/or resetting the iPhone:
If that does not resolve the issue, refer to page 146 in the iPhone User Guide to Reset All Settings:
iPhone User Guide for iOS 7
iOS 7 doesn't support all features on the iPhone 4 (it's too old and slow for several iOS 7 features), panorama photography and camera filters are among the features that are not available on the iPhone 4. Here's a list of what is supported on what hardware with iOS 7:
- Not all features are available on all devices.
- Traffic information in Today view is available on iPhone 4s or later.
- Panorama format is available on iPhone 4s or later and iPod touch (5th generation). Square and video formats and swipe to capture are available on iPhone 4 or later, iPad 2 or later, iPad mini, and iPod touch (5th generation).
- Filters in Camera are available on iPhone 4s or later and iPod touch (5th generation 32GB/64GB).
- Video sharing is not available on iPad 2 and iPod touch (5th generation 16GB).
- AirDrop is available on iPhone 5 or later, iPad (4th generation), iPad mini, and iPod touch (5th generation) and requires an iCloud account.
- Safari full-screen view and tab view are available on iPhone 4s or later and iPod touch (5th generation).
- Siri is available on iPhone 4s or later, iPad with Retina display, iPad mini, and iPod touch (5th generation) and requires Internet access. Siri may not be available in all languages or in all areas, and features may vary by area. Cellular data charges may apply. New female and male voices will be available initially in U.S. English, French, and German. Returning calls and playing voicemail are available on iPhone 4s or later.
- Find My iPhone enables you to locate iOS devices only when they are on and connected to a registered Wi-Fi network or have an active data plan. Some features may not be available for all countries or all areas.
- iCloud requires iOS 5 or later on iPhone 3GS or later, iPod touch (3rd generation or later), iPad, or iPad mini; a Mac computer with OS X Lion v10.7.5 or later; or a PC with Windows 7 or Windows 8 (Outlook 2007 or later or an up‑to‑date browser is required for accessing email, contacts, and calendars). Some features require iOS 7 and OS X Mavericks. Some features require a Wi‑Fi connection. Some features are not available in all countries. Access to some services is limited to 10 devices.
You laggy keyboard/typing issue however is another matter. Several iPhone 4 users (and other models too) have reported similar problems after upgrading to iOS 7, but most iPhone 4 users do not experience the issue. A fix I've heard has been successful in several cases is to logout of iCloud and iTunes and the App Store in Settings, reset the phone (press sleep/wake and home buttons together and hold until Apple logo appears), and then log back into iCloud and iTunes and the App Store in Settings again.