Hi, Mary. Since Windows Version 1803 was released in April and you have a new computer, yes. We can tell you how to go back if there are any issues. However, I would not expect your new PC to have a problem with the new version. Most likely, you'll be offered the Windows Build 1809 in the near future as well.
The process of upgrading to a new version is that after Windows Update starts the download, you can keep working. Don't turn off your computer. You will be prompted when it is time to restart the computer to install the update. Note that the installation process may take a while and it will restart a couple of times during that process. Just let it do its thing.