You can only delete a nominal account if it has never had any transactions posted to it. If a nominal account has previously been used, mark it as inactive instead. There is no option to do this in bulk — each account must be updated individually, using the steps below:
Go to the Membership tab.
Change the Secondary Reference description to something like No Longer In Use or Do Not Use.
Open the Attributes tab.
Disable postings from the Sales Ledger, Purchase Ledger and Cash Manager.
Close the nominal account by adding a date in the Closed field.