How to edit a ticket subject?

Hi,

I'd like to know how to edit the subject line of a ticket?

For example, if I am talking with a potential customer, and they then go on to place an order, I want to be able to update the subject of the current ticket, so that I can quickly find it in my list of open tickets. I don't need to remove or edit the ticket number - just the other text.

I think there must be a very simple way to do this, but as a newbie I can't see how.
I've tried Zendesk in the past and all you did was simply click on the subject and you could change it, no such luck with Zoho currently.

Any help appreciated!

Thanks

Dan