The lock symbol on the upper right hand corner

On an iPhone 5, the following from Rotate the screen on your iPhone or iPod touch - Apple Support is the only way that I know of.

Rotate the screen on an iPhone or iPod touch with a Home button

1. Swipe up from the bottom edge of your screen to open Contol Center.
2. Tap the Portrait Orientation Lock button  to make sure that it's off.
3. Turn your iPhone or iPod touch sideways. 

If the screen still won't rotate, try another app — like Safari or Messages — which are known to work in landscape mode.

Sorry, I've never heard of that. There is no option that I am aware of to remove that from Control Center. If someone else here doesn’t have information, you may want to contact Apple Support. There is a Contact Support link at the top right of this page.

If it is this symbol:   

That would be orientation lock (for screen rotation). See: Rotate the screen on your iPhone or iPod touch - Apple Support