Norah - thanks for replying.
Ash did tell me he'd changed my username from Quixote to another one at my request a long time ago - over a year - but I haven't logged on in a long time, and when I did a few weeks ago, it refused the new one and responded to my [forgotten your details?] click with an e-mail telling me that my username was still Quixote - which I've had to use to log on in order to send these messages to you.
I've tried starting over again to re-register in the new name, but it recognises my (only) e-mail address, and tells me I'm already registered - as Quixote - and won't proceed further!
So I'm stuck.
Ash did seem confident that he'd changed my username before (although he evidently hadn't); so I assume that he does have some means of doing so while retaining the same e-mail address for me.
I want to contribute to the forum, but not as Quixote, because I chose that name blunderingly, not realising until later that it was already the nom-de-guerre of a distinguished setter (now no longer with us), and it's therefore inappropriate for me to use it.
l look forward to further help - take care and keep safe.