When you building SharePoint based portals you will need to from time to time change the address of the SharePoint site.
Remember that only SharePoint Admin has the required rights to rename the site collection address.
Renaming SharePoint Online site URL
To rename the SharePoint Online site you need to open SharePoint Admin Center and change the site there. Thankfully Microsoft delivered this functionality. Thanks to that you are able to update site URL without any problems.
Remember that you need SharePoint Admin role rights to manage this operation. If you don’t have enougth permissions you will need to contact with yout IT team.
In the first step, you will need to is log in to Office 365
1. Open Office 365
Open Office 365 site using https://office.com address. In the Office site choose Admin button.
2. Open SharePoint Administration Center
When you will open Admin site choose Admin centers (1) and then SharePoint Admin Center (2).
3. Open New SharePoint Admin Center
In Admin Center choose Active sites (1).
3. Rename the site
Choose the site which you want to rename and click on the Site name.
In the new window choose Edit (1) button, next to URL section.
In the final step set the new address. The system will validate the availability of the address (1). After that click Save (2) button.
It will take a few minutes to update the address of the site. Previous address will redirect the users to the new site address. It will not be possible to create a new site using the old address.