How to UNLOCK rotation of the iPad 2 non retina
The Lock Rotation and the Mute Under the USE SIDE SWITCH TO: act as radio buttons.

Selecting one deselects the other.

Depending on which one is selected determines what the side switch does.

Either Mute or  Mute or Lock Rotation.

The side switch is either On (showing an orange dot ) or off  (NOT showing an orange dot )

In Mute mode: 


side switch ON = silent 
side switch OFF = sound


In Lock Rotation mode: 


side switch ON = No Rotation
side switch OFF = Rotation


The Control Center's  (when you swipe up) button that is used for  Mute or Lock Rotation will also change to either a Mute or Lock Rotation button depending what is selected in the settings.

So you have full control regardless of how you are setup.