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.
Backdoor.Andromeda is the generic detection for Trojans of the Andromeda family. There are many variants that all allow remote, unauthorized access to a system. Threat actors have a variety of modules at their disposal that can install other malware or steal information from the affected system.
This backdoor is usually spread by malicious email attachments or by exploit kits.
Malwarebytes can remove Backdoor.Andromeda without further user interaction. In case of active infection, it is imperative to find out if (and what) information have been stolen, so you can take countermeasures, such as changing passwords.