Debian 10 was just released and upgrading from Debian 9 isn’t as complicated as you might think.
Before you start: make sure you have backups and that any packages/software you use also has support for Debian 10 (otherwise it might be wise to wait).
First, create a backup copy of the /etc/apt/sources.list file.
Then open the file for editing (replace nano with your editor of choice).
Change all references from stretch to buster (example below).
Make sure you also update any other apt sources found in /etc/apt/sources.list.d directory (if your listed repositories has buster supported).
Update the local package list.
Then update all packages.
Finally, you can run the distribution upgrade.
Once finished, reboot your system. Running lsb_release -a (or hostnamectl) after reboot should display buster instead of stretch if performed correctly.
Congratulations! You now have a working installation of Debian 10.