How to change the font on the he time

Go to Settings > Accessibility > Display & Text Size. Adjust any of the following: Bold Text: Display the text in boldface characters. Larger Text: Turn on Larger Accessibility Sizes, then adjust the text size using the slider.

Adjust the display and text size on iPhone - Apple Support (IN)

You may get better and prompt responses if you may kindly provide the iPhone Model that you have and the iOS version if it is known to you and re-post.

With the limited information that you have provided, It is hard to even guess the problems faced by you. 

You may get faster and better responses to your query by --> Writing an effective Apple Support Commun… - Apple ...

Please re-post with detail so that someone else can help.

Lock screen Font change?

Please see the pic below which is self-explanatory