To delete a Contract you must fulfill some rules, based on its status:
If your contract Status is:
'started', not yet validated, then you can delete it at any moment;
'pending', you have to wait for your Seller to validate or reject it, no deletion during this period is allowed;
'running', you cannot delete it anymore;
'infringed', you cannot delete it anymore;
To delete a Contract go to your list of Contracts and click on the trash icon: