You can change subtitles size with Freemake Subtitles Pack. Follow these steps:
1. Open Freemake Video Converter.
2. Activate Freemake Subtitles Pack.
3. Add a video via +Video or +DVD button
4. Click the green button next to the video to launch the video player.
5. Select subtitles from the corresponding box or add your subtitles. Please make sure that subtitles format is supported. See the list of supported formats here http://www.freemake.com/packs/subtitles/
6. Play the video and click “+” or “-” sign to increase or decrease subtitles size.
7. Click “OK” button when you selected a suitable subtitles size.
8. Convert your video with subtitles to any format to save changes.
PLEASE NOTE that this guide is NOT valid for hard subs (that can't be switched off), subtitles in eastern languages and non-supported subtitles encoding.