Updating a Debian distribution is very simple and involves three main steps:

1/ Update your packages on your current distribution#

 root@Helpdesk:~# apt-get update && apt-get upgrade

2/ Update your sources.list file#

We back up the previous file (so you can go back if needed)

 root@Helpdesk:~# cp /etc/apt/sources.list /etc/apt/sources.list.old

We replace the Debian version name:

If you are moving from Debian 7 (Wheezy) to Debian 8 (Jessie)#

 root@Helpdesk:~# sed -i 's/wheezy/jessie/g' /etc/apt/sources.list

If you are moving from Debian 8 (Jessie) to Debian 9 (Stretch)#

 root@Helpdesk:~# sed -i 's/jessie/stretch/g' /etc/apt/sources.list

If you are moving from Debian 9 (Stretch) to Debian 10 (Buster)#

 root@Helpdesk:~# sed -i 's/stretch/buster/g' /etc/apt/sources.list

3/ Update the packages and the system#

 root@Helpdesk:~# apt-get update && apt-get upgrade && apt-get dist-upgrade

If everything goes well, you can then restart your VPS and check your Debian version:

 root@Helpdesk:~# cat /etc/debian_version10.7