iOS 7 is built to support iPhone 4 and up, and iPad 2 and later. Technically, this means iOS 7 should run smoothly in iPhone 4 and iPad 2 – the oldest iPhone/iPad devices with respect to iOS 7. But chances are high that your old iPhone/iPad stutters with iOS 7.
In terms of hardware, iOS 7 does run somewhat smoothly on older iDevices but other things – data, apps, processes running in the background, updates etc. can actually slow down your device.
Here are some tips to speed-up iOS 7 on your older iDevice such as iPhone 4/4S and iPad 2, 3, 4 and iPad Mini.
Stop Background App Refresh
iOS 7 refreshes apps even when they're running in the background. Naturally, this eats up a lot of memory when you run multiple apps that refresh automatically. In today's world, a lot of apps do this.
iOS 7 slowing down? May be cut down on the background app refresh. To turn this feature off, go to Settings → General → Background App Refresh and turn it off.
Turn Off Auto Updates
Looking at a large number of apps waiting to be updated isn't exactly nice but a lot of apps updating silently in the background isn't neat either – when you're on a limited data plan and on an old iPhone/iPad.
When enabled, iOS 7 will automatically update apps. You'll be notified, of course, but it keeps going on in the background along with all other processes. This could – at times – slow down iOS 7. If you have the habit of updating apps regularly – may be do it by the bedside overnight – you might want to turn it off.
Go to Settings → iTunes & App Store → turn off Updates under Automatic Downloads.
Clear Out Apps That You Don't Use
Smartphones need spring cleaning too. If you let your iPhone/iPad be a little disorganized, the app and data pile-up will cost a lot later. In the case of an old iPhone/iPad that runs iOS 7, this effect compounds. So it's better that you clear out apps from your iPhone/iPad. When you clear out apps and their associated data, you do get a lot of space that iOS 7 can expand to or make use of.