System (click the menu entry please)>Video>Subtitles
On some skins you may need to click on Settings, or Power/Exit/Quit then Settings.
Make sure subtitles are enabled, and also make sure “Languages to download subtitles for” only has English entered there. Finally Preferred subtitle language is set to English (you’ll need to scroll down a bit to find it).
Now, when you watch a video move the cursor and you’ll see the normal playback controls towards the bottom of the screen. One of these looks like a rectangle with a horizontal line at the bottom. If you click this icon (different skins may use different icons), you should be able to download subtitles there if they aren’t in the video stream itself. If the initial search doesn’t find any subtitles, press the right cursor a couple of times, and you’ll be able to try searching using the other subtitle service.
If the subtitle you download is not in sync with the audio, search again and try a different subtitle result.