Changing Default Text Size for Text Block

Hello! I apologize if this has been asked many times before, but I'm new here and I can't seem to find a solution.

Every time I open a new text block the default text size is paragraph 2. Most of the text used on my website is paragraph 3 and I'd like it to open as default in paragraph 3. Is there a way to do that? 

I have tried opening the text block, then changing it to paragraph 3, which works if I'm typing directly into the text block. But I do a lot of pasting over previous text and while the first line of text will paste in paragraph 3, the remaining text will default to paragraph 2. This means I have to highlight all the larger text and change it back to paragraph 3. And I do paste from Wordpad in Windows and I've also tried the Paste As Plain Text option, only to have the same result.