adb install -r <path to apk>

• -r replaces existing application
• If multiple devices are connected, specify the serial number of the device by -s option.
  The serial number of the device can be found like below.

  $ adb devices
  

Example:

$ adb -s emulator-5554 install -r /Users/pistolfly/AndroidstudioProjects/MyApp/app/release/app-release.apk