Hello,
See :
www.hikashop.com/forum/customers/891788-...as-guest.html#277482
Best would be to remove the "user_cms_id" in the HikaShop user table (for the account you want to remove) and afterwards you will be able to delete the Joomla accounts.
Thanks to that you'll keep the orders, the accounts will be transformed into guest account and they will be able to re-use the email for new guest orders.
For the rest, it's explained in the given URL.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.