When you log in with ftp, you already login to /home/username and then you see a folder called "yourdomain.com" and some mail folders if I remember right. So even if your the admin, you can't see your members uploads because they aren't in your user folder. (At least I haven't found out to get global access to my users yet, it might be possible)
If you go to Domains -> Re-map Sub Dir, you can change where your domain points. So for example,
www.domain.com/user1 goes to /home/user1/domain.com
www.domain.com/user2 goes to /home/user2/domain.com
It will take a hour or so to work properly. But be aware if you change a folder that already exists from www.domain.com/images to /home/user2/domain.com/images (where you are user1), you will have to tranfer the files from user1 to user2.
Hope you understand all that