How can I delete my activity in the forum and my profile too?

 

Well you have already deleted threads responses you asked question and received answers. So that sort of makes a mess of the forum. When you join did you read the rules and guidelines?

Contact the administrator or Moderator to remove or BAN your account. But I doubt he will remove your responses on threads you started and were answered on?
What you have done so far is considered RUDE on any forum.

If it were up to my I would Ban you and your ip address!

 

I would like to change the username on my new account. How do I do so? If I can't, how do I delete this account so I can start again?

 

send three potential new names here: https://www.mazdaforum.com/forum/sendmessage.php