I did a search for style change Heading 2 here in the forum but had a hard time finding any relevant, so I looked in the manual which gave me an idea to try out the following.
I am on a Macbook Pro where in general the font is small, and I like bigger fonts. I have changed the default font to be 18.
Here is an example of changing the font size of Heading 2. This can be used for making any change to any style.
Go into a document.
Write a word. Example Heading 2.
Go to the top format bar and change Heading 2 word to a bigger font size. I changed mine to 24.
Have the Heading 2 word selected.
Go to top menu: Format → Style → Redefine Style From Selection → Redefine Heading 2
The Redefine style panel pops up.
As the Redefine style panel is seen showing the Name, Shortcut, Formatting, Highlight Box and Next Style - click OK to accept the change. Then click OK in the next panel that shows up saying: The “Heading 2” style will be updated throughout the project.
All Heading 2 styles will be updated for the full project.
This makes it very easy to style some text with font family, font size and other style adjustments made through the format bar. Select the word/text and then redefine it to become a new style or to adjust an existing style.