How do I access the web management?

It depends where you are:

If you are on the server you just need to click on the web management icon.

If you are on a client or standalone computer in the internal zone you just type: https://xen:2001 or https://172.30.0.2:2001

If you are outside the school and you have it setup: https://mydomainhere.county.sch.uk:3001