Copy Site - Change the URL of your Site - classic Google Sites
Make copy of your classic Google Site to a new location, which means you can change the URL of your site (provided the URL you want to use is not already in use, deleted or reserved).
Sign in to your site and use the More button (looks like a cog or a gear) and then Manage site.
Go to the General page and scroll down and use the Copy this Site button
Enter the site name, your new URL, choose if you want to keep the revisions and sharing, enter the captcha code and use the Copy site button.
This will not redirect your previous site's URL to your new site: you will need to put a link on your old site to your new site to direct visitors to the right place.
This video is best watched in high definition and in full-screen: to do this make sure you have clicked the HD button next to the time line below the video and use the Full-screen button to the right of that.