How to change the subtitles font size in VLC Media Player

1. Open VLC media player.
2. Click the File Menu.
3. Click Open File.
4. Click Browse to Open the Movie.
5. Check the "Use a subtitle file" Box.
6. Click Browse to Open the Subtitle.
7. Click "Advanced Settings"
8. Move the Delay into the minus if the subtitles are too fast. Move it into the positive if the subtitles are too slow.

You can also just press H and G while the video is running to align the subtitles backward and forward in time; for the voice use J and K. The increments are in milliseconds, so it can be pretty easily fine tuned that way.

Source

If you want to fix the subtitles 'for good', I recommend Subtitle Workshop; it's free.