You can use the web interface to do that, but i had some issues soing so. It’s better (and much faster) to run this:
/bin/su -s /bin/bash -c 'cd /usr/share/python/scirius/ && . bin/activate && python bin/manage.py updatesuricata && deactivate' www-data
You can check your success by inspecting /etc/suricata/rules/scrirus.rules
To check the plausibility/validity of your rules it’s better to reload them via the GUI, it may show you some stuff.