how to move my itunes library from my PC to my iMac

Hi, I need to move my iTunes library off an old Windows laptop and on to my new iMac. The library is approx 100Gb in size. I searched and searched and can't believe Apple don't have an app for this. I found a third party app called CopyTrans TuneSwift which i read rave reviews about so paid my $15 USD for it and gave it a go. The backup worked well. Then came the part of downloading the Mac restore file. Once I tried to run this on the iMac, I recieved an error saying that the developer is not registered with Apple and could be a dangerous file.

I paid $4000 US for this iMac and yes I don't want to screw up the op system on day one. I can hold down the Control key and clicking to run the CopyTrans App to bypass the Apple security but I never want to do things like this... I want to keep the iMac clean and stable.

What to do now.

How can I move the iTunes library safely from my Windows laptop to my iMac.

Can anyone help.

Kind Regards