The very first step you should take when purchasing a design should be to backup the design after downloading the files. The example below was done on a Mac with the latest version of High Sierra.
Create a new folder on your desktop.
Rename the folder to something you’ll remember.
Right click the file you downloaded and select “copy.”
Go into the folder you made earlier, and right click, then paste the file into the folder.
Store the folder somewhere safe so you’ll always have a copy of your download.