Simply tap the End button on the Call screen to end the call.
If you accessed other device functions while the call was in progress, there are several ways to return to the Call screen to end the call.
Tap the Ongoing call icon (at the upper-left corner of the screen).
Tap the Home Button , then tap the Phone icon .
If necessary, you can drag the Ongoing call icon to move it somewhere else the screen while using other device functions.
Drag the Status Bar down, then tap the Current call notification on the Notifications panel.
You can also press the Power/Lock Key to end the call, if you activated this feature in the Call settings (tap the Menu icon in the Phone app).