Restart Your iPhone
One of the easiest ways to speed up your older iPhone is to restart it every now and then.
It’s always recommended to restart your iPhone at least once a week to keep its top-notch performance, but that doesn’t mean you need to wait. You can also restart it as soon as you start seeing some stuttering.
There are a couple of ways to restart your iPhone, but the fastest is to press and hold the side button and the volume up button at the same time for a few seconds.
If you have an iPhone with Touch ID, all you need to do is press and hold the side button for a few moments.
Drag the slider right below the Slide to Power Off message at the top of your screen.
After you restart your iPhone, wait a few seconds and then press and hold the side button until you see the Apple logo again.
If you can’t use the side button for some reason, you can also turn off your iPhone by going to Settings > General > Shut Down and then dragging the slider.