You can't delete control accounts - they are needed as the "Summary Account" for the sub-ledgers.
If you have not used any inventory (and don't intend to), go into setup..inventory...integration/groups. Change all the accounts to point to your sales/revenue account in group 001 - services. Delete the other groups, 002 onwards. Then De-select integrate inventory to GL at the top. You will then be able to delete the GL accounts, as they are no longer control accounts.
If you need to delete additional cashbooks, setup..entrytypes - change the cashbook number to zero for the additional cashbooks, then you can delete those GL accounts as well.