You can adjust the text size of Instagram through your device or browser settings.
To adjust the text size of Instagram:

Instagram app for Android
- Go to your device's settings.
- Enter your display settings to change the text size.
- Close and re-open the Instagram app to see the new text size.

Instagram app for iPhone
- Go to your device's settings.
- Tap Accessibility, then tap Display & Text Size.
- Tap Larger Text.
- Tap the toggle to turn on Larger Accessibility Sizes.
- Drag the slider to adjust the text size.

Instagram.com from a computer
- Use the built-in zoom feature for your browser holding down ctrl (PC) or command (Mac) on your keyboard.
- Press + to zoom in or - to zoom out.