Unfortunately, the Magnum Anti-Malware website seems to be inaccessible at this time and I'm not sure if it's a temporary issue or if the product no longer exists. However:
- ZAM - according to the information I could find, ZAM is actually Zemana AntiMalware, so this may be the security service that you subscribed to.
- UAC - the prompt that you receive, the one asking you if you want to "allow ZAM to change your computer", is a Windows security feature called User Account Control that has been introduced since Vista. Like every other antivirus / antimalware tool, ZAM needs to be able to make changes to your PC, so you need to click Yes on that prompt.
In case you still have issues, try contacting Zemana AntiMalware at this email address: email@example.com