1. Can you clarify what you mean?
2. You need to be Jira System Administrator to delete user with Jira System Administrator global permission. Take a look at this article About JIRA System Administrators and JIRA Administrators
To change your url, you need to raise a support request with Atlassian, over at https://support.atlassian.com/contact - until recently, they did not do url changes, but they do now, as long as you don't ask frequently. Choose your new url carefully, while it can be changed, it is going to be with you for a while.
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