Restoring Your iTunes Library on a Mac
Select the music file folder you have on your storage device (CD, DVD, External Hard Drive, or Network Storage space) and drag this content to destination folder on your new laptop (i.e. for most the iTunes folder for most users).
If you are replacing your computer, installing a new operating system or anything that will have you not use that iTunes program on that computer we suggest deauthorizing that iTunes application from your account. Apple only lets your account have a certain amount of iTunes applications installed. For example, your account authorizes 4 iTunes applications on 4 different computers.
You will need to deauthorize your iTunes account on the old laptop before you replace it and then re-authorize your account on your new laptop. To deauthorize open iTunes and select the Store tab – Deauthorize this Computer
General Articles on iTunes