The best would be to copy the wanted theme from there to ~/.e16/themes/ and give it an alternate name. That way you'l have full control of all changes and can always hop back to the original if you muck stuff up. 
It'll be somewhat like what I showed in part 3 of the tutorial here:
You'll be needing to change the size of the titlebar in it's .../borders/default.cfg configuration file as that doesn't dynamically resize with the changed fonts.
- Just changing the min and max height opens "new" issues like the size of the window buttons and the necessity for the left and right bars to accommodate the extra pixel height (to avoid it taking away space below). else you get a sort of Frankenheimer widget like the one below set at 25 pixels.
Themes differ in how they handle this, so it will be a matter of going through said file and changing the options. by trial and error.
If you want to read up on how E16 is configured and what needs to be edited, go here:
https://themes.effx.us/e16-Documentation.html
Not a lot but it gives a good impression on how E16 is built.
It's a steep learning curve, once you dive into that but it has it's perks if you plan to keep on personalizing and using E16. 
Happy modding.
