I got some newbie answer on using Aegisub.
How to resize the font size in Aegisub???
I have just recently used it, so I dunno how to resize the font.

Open the ass in Aegisub first.
Once loaded, click the "subtitles" tab in the task bar.
Click on Styles Manager. A window should open.
Doubleclick on "Default" (it's usually called default, could be something else too).
There you can make any change you desire.

Let me know if it worked for you!

well I just finished it yesterday by using notepad