Log into the routers interface click here If you are prompted to login, the default username is admin and the password is password. Click on Basic settings on the left you should see a field marked Login. This should currently show your ISP's log in details. You need to enter the bt-test etc into that field, no password is required. Then click Apply.
I presume they then want you to copy details of the overnight logs which can be accessed via the link Logs on the left hand side of the interface.
Make sure you have your ISP's log in details safe for when you have to re-enter them.