Bring up your keyboard - you should now see at the very bottom of the keyboard, something that resembles another keyboard. This brings up your keyboard options. From there, you will probably see that your keyboard is currently set to English - press the gear wheel to the RHS of your selected keyboard. Below this, you should see MANAGE INPUT AND LANGUAGES after you have hit LANGUAGES AND TYPES. You can now select Russian as your input language. Reverse the process to revert back to English.
