You'll have to use the explanation area of the 1040X to show change youre reporting, but up at the top of page 2 of the 1040x you should see the change in exemptions, even if the dollar amounts dont change.

Personally, I'd input the original and amended figures in the column on the front page of the 1040X (just type them in, use override if you have to)...I had one kicked back as incomplete when I was amending but no dollar difference happened so the 1040x front page was empty.