Steps:
Navigate to the "Account" screen, this can be done from either the bottom tab navigation bar or from the dashboard cards (if you have it included in your list of cards).
In the "Font Size" setting row, slide the slider to to fit the scale that you prefer. By default the app will use "1x" for the size. As you slide, the font size will automatically change so you can decide which size works best.
Note: your size preference is saved locally and is device specific. If you have the app installed on multiple phones and/or tablets, you can change the the setting for each of them.