It’s easy to copy your files and settings wirelessly from another Mac or PC to your iMac. You can transfer information to your iMac from an existing computer or from a Time Machine backup on a USB storage device.
You might need to upgrade the macOS version on your older computer before you can transfer the information on it—Migration Assistant requires macOS 10.7 or later, but it’s best to update your older computer to the latest version possible. If you’re not sure which iMac you have or want to find information about other models, see the Apple Support article on your 21.5-inch iMac or 27-inch iMac. Then drag files from the storage device to your iMac.
Restore your content. To learn how to restore your Mac from a Time Machine or other backup, see the Apple Support article Move your content to a new Mac.