How do I contact admin staff to ask them to merge two threads I started. Only one is required. 

We don't normally merge topics.

Best to close one with a link to the other one.

To close the thread that you don't want to continue, click on "Report post" and ask for closure of the thread.

One of the moderators will then take care.

What about the complete removal of a thread? Is this something that mods will do - if politely asked by an OP?

16 minutes ago, Gregster said:

What about the complete removal of a thread? Is this something that mods will do - if politely asked by an OP?

Yes it can be removed.

Yes it can be removed.

 

Do I send a PM to any mod for a request to delete a thread? Must I give reason/s why?

27 minutes ago, Gregster said:

 

Do I send a PM to any mod for a request to delete a thread? Must I give reason/s why?

If you are the OP you can do a report of your topic requesting it be removed. A valid reason will help the mod to decide on removing it.

In some cases it is best to close it instead of removing it.