Hi,

1/ For translate "Leave A Reply" text - you can try translate it via Customize > Quick Text Translation > "Leave A Comment" - check this image: http://prntscr.com/xh7tbv

If it doesn't work, it seems you're using a plugin to modify your comment and it modified that text also, and you need to check the settings from that plugin to find a way to do that.

2/ To do that, please go to update the theme to latest version 7.6.1

To update the theme to latest version - please remove the code at the end of functions.php file like on this image: http://prntscr.com/uon4qx ( if you don't see it, you can ignore this step ) 

After that, do following this guide to get auto-updates the theme: https://pencidesign.ticksy.com/article/15633/

When you have done, go to Customize > Posts Layouts > Font Size > and change it there.

Best Regards, 

PenciDesign