1. On your Keyboard, hold the settings icon

On your Keyboard, hold the settings icon (like in pic below, not my pic). Then click switch input method, a list will come up whit all activated keyboards. Choose one and then your keyboard changes. All without the need for an external app.

2. Scroll Down and click "Change input method"

3. A list will come up with all activated keyboards. Choose one and then your keyboard will change to the selected keyboard. All without the need for an external app.