How do I swap out old content/theme for new?

If you want to start a new site from scratch, but still have the old site accessible to visitors while you work on the new one, you may want to consider creating a new subdomain and installing a new WordPress instance there.

If you’re not sure how to do that, you may want to get into contact with your host, as they likely have documentation / instructions to help you do that.

You can make your changes in stages.
In the admin menu, under Appearance, is Customize. That lets you preview your site with different themes. So you can make the theme change before you start in on the content rearrangement.
As for plugin problems, you should fix that independently of the content. That would only transfer to a new site if you put the same plugins.
But you don’t really need a new site, especially as you want to keep your domain name.

You can install WordPress on your computer and mess around as much as you want. It’s easier than setting up a subdomain and working online (you can also install in a folder, it’s easier).
You can export your current site and import it into your working installation, or just copy and paste the parts you want to keep.

If you do decide to make a new installation, you’ll get it all looking the way you want, and then use a migration plugin to get it to the original site. The migration plugins usually ask you what you want to change, like domain name, and they make the change for you in the database (everywhere like links and options and images). So if working on localhost, it would change localhost to ellemottauthor.com as it migrates the data.

Thank you, Joy. This brings some clarification. I see now in Customization, this is where I can change my theme— now, to adjust everything in my choices in Customization, I would do this after changing theme, right? And in changing theme/customization, does my “old site” (lack of techy words) stay alive until I “publish” the new theme? You’re the first answer I’ve found as to if the plug problems would transfer as well. Will it work if right before I go live with all that is new to then fix plug-ins? I’m thinking plug ins vary by theme (??) Is a “new theme” the same as a “new site”? (I’m confused there—I didn’t think it was / I don’t know techy terms.) Re: installing WordPress on my computer, there must be something easier than WAMP – I already tried that but failed, couldn’t figure out how to access it after download, so I removed it. I don’t need to export if I am changing Pages and content, do I? (I have a mock site in MS Word to copy/paste from). What about a subdomain as Carike suggests—will that work in lieu of WordPress on my computer? The migration link/form you provide – is that for moving stuff from WordPress site on my computer to the new theme? (I’m not clear.) Thanks. I figured I could learn this for lack of money to hire someone.

to adjust everything in my choices in Customization, I would do this after changing theme, right?

The Customizer lets you preview your site with other themes, but you can’t change any options the new theme provides without changing over to it. (making that theme active)

And in changing theme/customization, does my “old site” (lack of techy words) stay alive until I “publish” the new theme?

Your site can only have one active theme. That theme is used to display the front end of the site (what visitors see). When you are in Customizer, you can change the active theme’s options and see the preview. Those changes are not seen by visitors until you Publish them.

Will it work if right before I go live with all that is new to then fix plug-ins?

It depends on what the problem is. You should ask at the plugin’s support forum if you are having a problem with a plugin. Or remove the plugin if it’s not doing what you want. Plugins have a state: activated or deactivated. They run on every page request, but only if activated. This is unrelated to changes you plan to make to your content.

I’m thinking plug ins vary by theme (??)

No. Themes are independent from plugins. Themes in the WP repository cannot require plugins to work.

Is a “new theme” the same as a “new site”?

No. A site is a domain name and all the pages that comprise it. A theme is some code that styles and outputs the content that your site has stored in the database.

Re: installing WordPress on my computer, there must be something easier than WAMP

There is Local by Flywheel, but I’ve never used it.

I don’t need to export if I am changing Pages and content, do I?

No. I mentioned export so you would know one way to have your content if you install a testing copy. (you can also use a migration plugin)

What about a subdomain as Carike suggests

It can work just fine, but you have to set it up. You definitely will need a migration plugin to move the content from there to the original site. Any time you are moving a bunch of content to a different domain name, then a migration plugin will do all the name changes for you, whether that is sub.domain to domain, or localhost to domain, or domain to sub.domain.

Thank you so much, Joy. I will move forward from the help you’ve given.