From the FTM 2011 Help file (the procedure is the same in FTM 2010):
To merge two people
1. From the People workspace, select the person you want to merge to. This is "individual 1." You can select the person in either the…"
"Thank you, Russ. I will contact them in the morning. I am able to edit the tree.
I did find this in the Help section: "Your My Account password is not necessarily the same password you used for a tree or on the message boards." I…"
My suggestion is that you contact Ancestry.co.uk. I don't know how they operate. But if you are seeing your tree in the Web Dashboard and you open a Browser window, you should be able to do anything to your Member Family Tree.
"I downloaded the tree to FTM 2010, then tried deleting the tree on Ancestry. Unfortunately, I still get the "incorrect password" error message. I am entering the same password as I am logged into Ancestry with."
Then, guessing that you registered and are online with the SAME UserID and Password, you should be able to Delete your Member Family Tree AFTER you have downloaded in into 2010, from online.