Originally Posted by
Zulandia
So is it the floating combat text (those numbers that pop up around your target) or the scrolling combat text (the ones which roll down the right side there) you want to change? Also out of curiosity do you know which addon you are using? If I had to guess (and I'd rather not as they all can be made to look the exact same) I'd say you are likely using Mik's Scrolling Battle Text in which case if you type /msbt you'll be able to edit it that way (font, size, behaviour everything).
Your floating combat text however appears to be the default one, some basic elements of this can be changed by going esc > Interface > Floating Combat Text, however to change more in depth things you will need to either get an addon or change the font for all of WoW (there are many sources which can tell you how to change WoW fonts if you just google, but note this will change the font anywhere it is used in WoW. The size of the font can also not be changed this way.
In completely unrelated news why do you need both scrolling and floating text?