Nokia Lumia 720

Find "ringtones+sounds"

Slide your finger left on the display.
Press Settings.

Find "ringtones+sounds"

Press ringtones+sounds.

Select your ring tone

Press the field below "Ringtone".

Select your ring tone

Press the play icon next to the required ring tones to listen to them.

Select your ring tone

Once you've found a ring tone you like, press the required ring tone.

Return to the home screen

Press the Home key to return to the home screen.