Welcome to the forum.
With individual Titles, I do not know of a way to globally change them all, with one operation.
However, you can come close - create a new Style (or choose one that matches your needs), save that Style, then apply that to the Selected Text on each Title. That will be on a one-by-one basis, but is quite quick, and you will edit most attributes of your Text, with but one click - the application of the newly created Style.
Good luck, and hope that helps,
I also am not aware of how to change all titles at one time with regard to the same font style and font size in one operation.
Hunt's suggestion of a "new Style creation" is an interesting one. But, I would need to think through potential individual font size corrections as a consequence, especially if the original varied from text title to text title with regard to font style and font size.
Please let us know what works for you.