Do you mean the on-screen size or on the printed output when you print the pdf?
If all you want to do is to increase the size of the screen font then the slider with + and - at the bottom centre of the work area allows you to increase the font from barely visible to about 30-40pt on the screen - at least on my small laptop. Maybe bigger on a 27" Mac. At that size you'll see just one or two boxes at most. So just adjust the sliders to what is comfortable for you.
If you want to increase the font size in the input panel on the left hand side of the work area you can't unless you play with your screen settings to adjust resoultion and screen settings.
If you want to increase the size of printed text on the final hard copy output that you make from the pdf that the software generates you'll have to do some calculations. In my case the file that this system generated for me printed onto six 8.5 inch x 11 inch (American Letter size) sheets oriented landscape. I had over 200 names over 7 generations. On those sheets each box had text that was no more than about 7pt or 8pt and hard to read. Even though each box only had a name and birth-death date.
And I really didn't want my final output barely readable on pasted together sheets, I wanted it on one single sheet. I then had to estimate how long and tall that one sheet needed to be. Even with a printout equivalent in width to six letter-size landscape-orientated pages (i.e. 51 inches x 11 inches) I got everything on one sheet of paper but it was not much improved in font size - say up to about 9-10pt. So wide and narrow to fit everything onto a single sheet but just readable comfortably. This of course had to be printed off at a commercial printshop with roll-fed printers, which may not be easily available to everyone.
One drawback is there was a lot of wasted white space at the top and bottom and the words My Family Tree appeared in about 120 pt font across the top - ugly. There doesn't seem to be any way to change that setting.Or to change the size of the boxes execpt by including more facts and photos - they then resize to fit the information.
It's likely that you could export the data into another platform to get more flexibility but there may be a subscrition cost attached to that. And if you were tech savvy you could probably convert the output into some graphic format with individual moveable objects to arrange them as you wish. But I heven't even looked at that.
So that's my experience - and I hope it helps anyone who is struggling .
