I'll use the Swap Shop as an example.
When you upload something, you put your item onto the Swap Shop. That's it.
When you download something, you take someone else's item from the Swap Shop.
Think of it like this. You've probably heard of the cloud, which is (as I understand it), a gigantic storage space.
If I upload something, I send it up to the cloud so that everyone can get it.
If I download something, I take a copy of it down from the cloud.
What you're describing is simply installing Max.
In short, using you as an example:
Upload = Leto puts Max onto the forum.
Download = Magz takes a copy of Max off the forum.
Install = Magz takes their copy of Max from the forum, places it in their game, and installs it using the Launcher.
