When the aMule window opens, click the "Preferences" button:

 When the aMule window opens, click the Click to Enlarge

On the right toolbar, click on "Connection." Set "Upload" to zero kB/s:

 On the right toolbar, click on Click to Enlarge

Under the "Files" taskbar, ensure that "Add new shared files with auto priority," and "Try to transfer full chunks to all uploads" are unchecked:

 Under the Click to Enlarge

Under the "Statistics" toolbar, ensure that uploads are set to the minimum. In the case of aMule, the minimum is 3 kb/s.
To avoid uploading, you can cancel uploads in progress on the home page:

 Under the "Statistics" toolbar, ensure that uploads are set to the minimum. In the case of aMule, the minimum is 3 kb/s. To avoid uploading, you can cancel uploads in progress on the home page:Click to Enlarge

Under the "Advanced" taskbar (on the right-hand menu), drag the slider bar to the farthest left.
This will, to the maximum extent allowed by aMule, limit uploading:

 Under the Click to Enlarge