Trojan.Agent refers to a generic Trojan malware detection. It is used for detections that are either associated with no specific malware families or not enough information is available to pinpoint the malware family.
This Trojan is mostly delivered by mail as attachments or as a link to an infected site.
Malwarebytes can remove Trojan.Upatre without further user interaction. You can expect to find additional malware on a system if this Trojan has been active.