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.