To get the list of process instances:
POST api/enterprise/process-instances/query
with a json body containing the query parameters. The following parameters are possible:
- 
processDefinitionId
 - 
appDefinitionId
 - 
state (possible values are running, completed and all)
 - 
sort (possible values are created-desc, created-asc, ended-desc, ended-asc)
 - 
start (for paging, default 0)
 - 
size (for paging, default 25)
 
Example response:
{
        "size": 6,
        "total": 6,
        "start": 0,
        "data":[
                {"id": "2511", "name": "Test step - January 8th 2015", "businessKey": null, "processDefinitionId": "teststep:3:29"...},
                ...
        ]
}
To get a process instance:
GET api/enterprise/process-instances/{processInstanceId}
To get diagram for a process instance:
GET api/enterprise/process-instances/{processInstanceId}/diagram
        To delete a Process Instance:
DELETE api/enterprise/process-instances/{processInstanceId}
        To suspend a process instance:
PUT api/enterprise/process-instances/{processInstanceId}/suspend
To activate a process instance:
PUT api/enterprise/process-instances/{processInstanceId}/activate
Where, processinstanceId is the Id of the process instance.