If after installing iOS 11 you have problems with the iPhone slow here are some tricks that could speed up the device, also valid on iPad and even on previous operating systems.
Wait
First of all, the first advice is to wait. After installing a major upgrade it is normal for the system to tend to be slow for the first few hours. In addition to downloading apps, in the background iOS works to recreate the Spotlight search indexes, which requires access to memory and compute power and that can for a long time, depending on the number of photos, email apps and more on the device. So, even before setting the settings, it might be enough to wait a little, even one day.
Free up memory space
It may seem trivial, but it is so. Installing applications and games without ever deleting them is a real boulder that weighs on the available memory of the device and on performance. App Store is chock full of interesting apps to test, but over time you risk losing control of what was installed on your device. For this reason it is sufficient to access the Settings menu, General, enter the free Space tab iPhone and check all that is installed on the terminal. Next to each app or game shown in the list, the weight of each application will also be indicated. Simply select those that are no longer used and delete them.
Disable unused functions
iPhone and iPad with iOS 11 are full of new features, many of which could slow down the device, especially if it is not the latest generation of devices. For example, you can turn off the motion effect from the Accessibility menu by turning on the Reduce Motion switch. Transparencies can also be reduced from the Accessibility menu, within the Increase Contrast tab.
Turn off app updates in the background
To save battery on iPhone and iPad, you can also disable the app update in the background. To access the menu, and disable app the update in the background simply go to Settings, General, Update app in the background.
Disable automatic app updates
Still, the advice is to disable automatic updates to the app, going to Settings, iTunes and turning off the Updates switch under the heading Automatic Downloads.
Disable location services
Even if the localization services are particularly useful in the case of theft or loss of your device, these reduce the reactivity of the device, in addition to weigh a considerable amount of battery life. In fact, there are many applications that use localization services in the background to determine the position.
Go to Settings, then Privacy, then to Localization, you can choose to disable them completely. However, it may be advisable to deactivate only the location services for some applications, such as Facebook, for example, where sharing your position is not essential. On the contrary, in some applications like Maps, it is absolutely necessary to keep the location services active.
Reset Settings
If the above does not work yet you can try to reset all settings on iPhone and iPad. This system will NOT erase the contents of the iPhone, but will only initialize the settings. To do so, simply go to Settings > General > Reset.
Completely reset the phone
As the last solution, you could try to initialize the device. This will erase all content on the iPhone or iPad. To attempt this extreme route you need to go to Settings > General > Reset > Erase all content and settings.