Always ask before making changes for someone else. They might prefer things the way they are.
Text size adjustments have been around for a while now but they tend to be hidden in the settings menu. Here are some instructions and quick demos to show you were to find them for most major devices:
Always ask before making changes for someone else. They might prefer things the way they are.
Changing font sizes can have unintended consequences for some apps. It might result in more scrolling, odd-looking alignment of text or text that cannot be read because it is cut off. These are rare but it is wise to test your changes in your favorite apps.
For some, text size may only be one piece of the puzzle. There are other accessibility features that can be helpful. Consider checking in with your state's Assistive Technology Program if you have questions.