This can be risky so back up any folders on your new computer before starting this process! Note: this will only copy contents in the CC Manager - not any other downloads you have loose in the Mods folder.
- Install The Sims and all your expansion packs on your new computer
- Install the TSR CC Manager and run it for the first time just to check all is okay and it can find your new game folders
- From your old computer, copy these two folders in entirety onto a USB stick or external drive
- Documents\Electronic Arts\TSRCCManager
- Documents\Electronic Arts\The Sims 4\Mods\TSRLibrary
- Connect your USB stick or external drive to your new computer and now transfer the folders to the exact same locations on your new computer.
Open the CC Manager and all your downloads should be present. If they're all on the DOWNLOADS tab, you'll need to install them again but, if you followed these steps correctly, your installed content should look identical to your old computer.
Note: you can also transfer your files over network if both computers are linked on the same network and visible to each other. You might need to enable network file and printer sharing and also mark both old and new computer drives as 'shared' to make them visible to each other.