Having trouble downloading rekordbox on my iMac

Hey guys,

Having some problems trying to download rekordbox. I'm a novice with my mac, had it 4 days.

I had rekordbox on my windows pc, but when i go to download on my iMac i get this message.

Authorization of the computer’s administrator is required to install and uninstall rekordbox. Log on as the user which was set as the computer’s administrator before installing.

Any help at all?