For those who don't realize it, Microsoft comes out with a brand new version of Windows 10 twice a year.
Version 1703 was released in spring 2017.
Version 1709 was released in fall 2017.
Version 1803 was released in spring 2018.
Version 1809 was released in fall 2018.
Version 1903 was released in spring 2019.
Version 1909 was released in fall 2019.
The rather confusingly named* Version 2004 came out a week ago.
If you want to upgrade from an earlier version of Windows 10, you can go here and click the big blue "update now" button:
If you choose to upgrade, you should probably wait until you don't need to use the computer for a period of time. The upgrade process will probably take awhile.
It also might be worth waiting until after the next Patch Tuesday (which will be June 9) so they can fix any bugs that crop up in the new version.
* If you think "Version 2004" is going to cause confusion, wait until "Version 2010" comes out in the fall.