Welcome to the HP Support forums. I understand that your print jobs from Photosmart 5520 seems very small.
The font size is controlled by the software program that the document was created in, for example any Microsoft Word document that you send to the printer the font size would have been chosen in Microsoft Word. I've included two different documents on how to change the print settings; one for Mac and one for Windows 8. These documents will show you the process on changing print settings if not the actual steps as you may not be using one of the operating systems mentioned.