This set of steps will show you how to increase or decrease your text size on your IOS 8 device.
Step 1: Open Settings
Go to settings app.
Step 2: Open Display & Brightness
Go to the Display & Brightness option.
Step 3: Go to Text Size
Go to Text Size option.
Step 4: Adjust Text Size
Adjust the the text size, slider to fit your needs. If you move the slider to the right it will increase the text size. If you move the slider to the left it will decrease the size of the text.