Changing Post Title Font In Twenty Fifteen theme

Hi there,

I have imported my files from Blogger to WordPress. Unfortunately, I am not sure how to change the post title of my previous posts, and any new posts I create have a post title font size that is too big. I am not very skilled in this area.

Does anyone know where and how I could change the font size of my post titles?

Thanks for your support.

David Cosier
livingandactivewords.com