First backup any DB's you need. Next uninstall the old version:
sudo apt remove postgresql-9.5
and install the new version
sudo apt install postgresql-10
Now edit the conf file to change the port for version 10 to 5432 as mine was set to 5433
sudo nano /etc/postgresql/10/main/postgresql.conf
# Press ctrl+w and search for "port"
# change it to port = 5432 and save
Now restart the service
sudo service postgresql restart
And now postgres should be 10.x!