How to enlarge print on printer from my Mac Book Air?

CT's suggestion to look at the app where you are printing the text from and see if they can change the font size before you print is the best suggestion.

After that scaling the document via the Print dialog box may work, but sometimes it just causes the output to exceed the paper size. It would be best to first print to "Preview" so you can see the effects your font size and or scaling changes things.

If you tell us what app you are printing from, maybe someone can give guidance on ways to increase the font size

It depends upon your printer and what kind of document you are printing. Maybe you can change the size via the app that creates/views your document. One thing you can usually do is change the "Scale" box in the printer dialog: