You have two ways to turn subtitles ON/OFF:
ONLY FOR THE CHANNEL YOU ARE CURRENTLY WATCHING:
Press the OPTIONS button, select SUBTITLES and indicate your preference using the righ/left arrow buttons, then press the OK button.
FOR ALL CHANNELS:
Press the MENU button and select PREFERENCES > LANGUAGE OPTIONS > SUBTITLES and indicate your preference using the righ/left arrow buttons, then press the EXIT button.