How do I delete used services

In the event that an app misbehaves or freezes, closing the app can be helpful. So that you know how to do this in the future, take a look at this.

Close an app on your iPhone or iPod touch - Apple Support

What do you mean by "used service"? Where are you seeing this?

dawsonnl wrote:

How do I close open apps

There is no need to close apps. Only one app can be active at a time. All the others are suspended.