No, if you bought your own domain address you cannot change it on an existing website. However, you can buy a totally new domain address if you want to, back up your present website to your computer, then upload the info again into your new domain name.
Here is a tutorial on backing up your website: Backing Up Your Website

What about if it is just the free domain and I haven't bought it yet? Can I change it then?

You just can't type in a new domain name for an existing free website, no. But you can get another free website here at SiteRubix with a new name, and move your info to the new free website.

Also, you can move websites to WA and here is the best tutorial I can find on this subject. How To Change Website Title and Tagline

Thanks for visiting my video. I plan on putting more together soon.

Yes, sometimes we forgot how to do the simplest things. Glad the video helps.

Thanks for watching my video.

Thanks for watching my video. Still learning but it was fun.

Thank you anyway, but I didn't cought nothing of what you said.

Thank you, Lucille2

It's very simple. To change your website title or tagline just do this:
dashboard/appeareance/customize/site identity/change site title or tagline