For those who use K-Lite codec pack (Media Player Classic and DirectVobSub).
If your subtitles look small then follow this steps:
Double click on DirectVobSub icon

DirectVobSub taskbar icon
The following window will appear. On the field “Text Settings” click the button “Arial”

DirectVobSub Properties
Again, click the button “Arial” on the field “Font”

Style editor
Now, you can change the color, size, font of the subtitles

Font
Thats all.