No, you cannot. We do not have a feature to delete chat messages, yet.
The conversation gets only deleted when:
The other user has removed you from his/her list or the other way around (chat will be transferred to archived list).
The other user has been banned from the app (chat will be transferred to archived list and a banned user indicator is visible).
The other user permanently deleted his/her account (chat will be gone and will leave no trace in the app).