I can probably help you figure this out, but I have some questions:
-
Which one of these do you mean?
A) There are photos in your family tree, and that the photos are too low quality.
B) I am trying to print the famly tree as a photo, and the tree in general is too low quality?
-
Where are you trying to print the tree? (home, Walgreens...)
-
How are you getting the PDF?
-
How are you converting the PDF to JPG?
Those answers will help us understand why you are not getting the quality that you expect. But a relatively easy way to get a higher resolution image would be to choose A0 paper instead.
You might find this answer useful, but it doesn't really address your specific question.