First, make sure you have a current backup of your data files. See these instructions:
Please note if you purchased the download of MasterCook 15 from MasterCook.com, you have a download link for the installation file in your account here: Downloadable Products.
Additionally, there are several online places that sell the MasterCook download. If you purchased it somewhere else, such as at Amazon, you need to use the download link you purchased from them since you are their customer. We do not have access to their customers or orders. For example, you will find your Amazon download link in your Games & Software Library.
Otherwise, you are welcome to provide proof of purchase by providing a copy of your receipt, and you can purchase a backup/replacement of the MasterCook 15 product at a discount at MasterCook.com. Send your request and proof of purchase to firstname.lastname@example.org to inquire.
Use that to download and install the program to your new computer. Run it and make sure it appears to have installed correctly. For example, do you see the cookbooks that come with the program in the Cookbooks screen?
Then you can merge your backed up files into the program on the new computer as explained here: MasterCook 15 Merge