User wants to clear the Chart of Accounts that come with Core by default and set up their own company accounts.
You cannot delete some of the system-generated accounts as long as they are set as the default accounts in Core. You can create your own set of accounts, but then you need to set them as the default accounts in Global Settings before you can delete the default ones that come with Core. Check out this article for details: Changing default accounts in Core. You may also want to check out the Core Help and the following links: