I always use the hypershade to delete a link (window->rendering editors->hypershade).
Manually creating links is indeed very annoying Maya, so I almost never do that.
But using the hypershade and the attribute editor most link related things are easy.
In the hypershade window, select one or more shaders and then clink on the >> to expand them (under 'graph', see image).
This way you can easily see all connected parts to a shader.
Then I click on the attribute editor (with material selected) and assign a new color texture to it.
By clicking on the color to add a new file.
Add the file to the shader like this (click on red square):
Attachment:
hyper2.jpg [ 466.3 KiB | Viewed 19010 times ]
After that select the 'file' as render node and click on it.
Then fill in the filename.
Select the shader and expand it using the >> in the hypershader window to see if the links are now correct.
Hope this helps.
Also look for tutorials on this.