I cannot see the "select input method" command in the pull down menu like in Android 4. By experimenting, I discovered you can select the input method if you long-press the space bar in Samsung keyboard. I used this to switch to Hacker's keyboard. But that keyboard doesn't support the space bar long press convention. So, I cannot change back.
Edit: the long press method is a feature of Google Japanese Input, not the Samsung Keyboard, sorry. I can change the input method via Settings/Language and input/Default Keyboard. That is far too inconvenient for regular use.
Edit: I remember seeing on some Android version a good mechanism for this: a little keyboard icon displayed while in input mode. I feel it must be somewhere; I'm just not looking in the right place.