Clearing your device's memory can help improve your device's speed to make it go faster. Your device may become slow because it is low on memory.
1.
From within the Settings app, tap General.
2.
Tap iPhone Storage.
3.
From this screen, you can perform a variety of actions to manage your device storage:
Offload Unused Apps - Enable this feature to automatically offload apps you haven't used in a while when your iPhone becomes low on storage. Associated documents and data will not be erased.
Manage apps individually - Select an app to view a breakdown of all storage data it's using. You can also offload or uninstall the app manually to save space.