You already know how to change the font size in messages on HTC 10. But what if you want to change the font size in the entire interface? To change font size in HTC 10, do as follows:
1. Open the Settings app (Use the notification panel to reach the Settings shortcut)
2. Scroll down to the Personal settings and tap to open the Personalize settings
3. Under the Font settings, touch to open the Font Size settings
4. Now, select the new size for the fonts displayed on your HTC 10, from Small and Medium to Large and Extra Large.