To delete a contract in BSI, you would go under "Administration" and "ACE management", then select "Purge".
You will see an option there to purge a contract.
Keep in mind this will simple trigger the ACE instance that was calculating this contract to begin the purge process.
So first, the ACE instance that was calculating this contract will need to run. This will flag the contract for purging in the database.
You can see this if you run:
select sla_name ,sla_status ,is_psl_purge_completed, is_penalty_purge_completed, is_data_to_be_purged from t_slas
If the PSLwriter has run then you should see this contract is now flagged "to_be_purged".
The service which will then actually complete the contract purge is the taskhost service. So this service needs to be running.