It is wise to erase / clear call history before handing over the mobile to some one or before selling out your mobile device. This is just the 5-step easy process in Android 5.1 Lollipop devices.
If you need help, go through the instructions.
Instructions
1: Tap the icon of the ‘Phone Dialer’ on the home screen of your Android 5.1 Lollipop device to open up the ‘Phone Dialer’ screen.
2: At the ‘Phone Dialer’ screen, tap the settings button, placed at the top right corner of the screen. It will open up a popup menu.
3: Tap ‘Call History’ in the popup menu.
4: At the ‘History’ screen, tap the settings button, placed at the top right corner of the screen. A small popup, ‘Clear call history’ will instantly appear.
5: If you want to clear all call history, just tap the popup ‘Clear call history’. It will erase all call history from the phone memory.
That’s all!