Hi Claudia
Please can you expand upon your question ?
I assume that you're referring to tasks that you've completed via the Process Portal ? Is this the case ?
If so, are you trying to remove the completed tasks from the BPM database ?
If so, take a look at the BPMProcessInstancesCleanup command - https://www.ibm.com/support/knowledgecenter/SSFTN5_8.5.0/com.ibm.wbpm.ref.doc/topics/rref_BPMProcessInstancesCleanup.html
In addition, you may wish to review the "Delete task on completion" checkbox in Process Designer, in the context of system tasks - https://www.ibm.com/support/knowledgecenter/SSV2LR/com.ibm.wbpm.wle.editor.doc/topics/implementing_activities.html
Hope this helps, Dave
With thanks
Dave Hay MBCS CITP
BPM Capability Lead
IBM Systems Middleware
Mobile : +44 7802 918423
Eddress : david_hay@uk.ibm.com