How to remove preinstalled iOS apps?
You can delete preinstalled iOS apps by holding down on the app icon until they wiggle, then choosing the × button. However, note that this will not free any space on your device as the apps are part of iOS and their files are not removed from your device. Removing any apps, regardless of whether they are part of the OS or not will not increase the speed of your device.

You can determine what is taking space on your device in Settings → General → Storage &amp; iCloud Usage → Storage: Manage Storage.