How to reduce font size manually?

I am doing a blog post and highlight only a specific sentence and then when I hit "Paragraph" and in drop down, choose h1, the ENTIRE or WHOLE post goes to that size. If I go into my text editor while that sentence is highlighted, what to wrap that line of text in? Let me know and thanks - NO PLUGINS....have enough of those

 

You are facing that problem because your text is not formatted. You just need clear all formatting of your text and then only possible to apply different options.

Just check below image, I am trying to make heading "A quick brown fox" only but after changing to H2, whole text changed as H2 because I forgot to clear text formatting and it's spacing as well.

So to make it work you just have to clear all formatting and spaces then after apply what are you trying for,

 

If you know html then you can change the coding from the text editor itself.

http://www.w3schools.com/TAGS/tag_font.asp

 

I think you're facing this problem. All you need to do is hit enter like in this video.

 

What I personally do, I first paste anything in notepad, this removes any kind of text formatting. Then I reformat whatever I want. You also can follow this way.