I can understand wanting to adjust your text sizes. Here are some steps to be able to adjust the text size.
1. Start the Settings app.
2. Tap "Display."
3. Tap "Font size and style."
4. Change the size of the font by dragging the Font size slider to the right or left. If you want to make all of your system text bold, turn on Bold font by swiping the button to the right.
In messages, if you want to adjust the text size pinch the screen, similar to zooming in or out on a photo and the text size with change for you.
Let me know if this helped!