Click on the 'Edit' link to the right of your organisation's entry.
If you see the words "No password is currently allocated for this organisation" it means that you need to apply for a password instead. See 'How can I obtain a password for an organisation that is listed here?'
Assuming you see a request to 'Enter Password' you should enter your six-digit number and press Submit. (A 'forgotten your password?' facility is available if you need it.) Provided that you have entered the correct number you will see an 'Edit Your Entry' screen. Make any changes necessary (taking care that any compulsory entries, indicated by a * next to them are completed) and press Submit.
This will give you an 'Updated Entry' screen, so that you can verify that you have entered the correct information and check that there are no error messages displayed. If the entry has been accepted you can now click on 'Back to List' to see your revised entry on the website.