Only Administrators can delete Jobs. 

For more information on Administrators see 

Adding a User.
 
When a Job is deleted, all the tasks and time spent on those tasks are also deleted.  If this is not what is required it may be better to Finish or Dispatch a Job.

For more information see

Finishing Jobs

Dispatching Jobs.
 
 
To delete a Job, from the Main Management Menu go to Job > All Jobs.

   

Click on Delete next to the Job Number you want to delete.