cannot edit fields

We've taken out a trial of Zoho CRM. I've used Zoho CRM before and on the other site I could always goto Setup/fields and I'd have an edit button beside each field. But with the new site I don't.

I thought it would be a permissions issue, but I'm logged in as super administrator, and I can find no permission that changes this.

I also thought it may be because of being a trial, but the first 15 days of a trial are the ultimate version, so Im thinking this is not the reason.

Is there a permission I'm missing somewhere?

Any help appreciated.

Kerry