I'm inclined to think Flatfender is right; I'm well familiar with the more modern rapidfire-type shifters, they're dead easy.
This one has no access hole at all...
The number-indicator cap has a couple of phillips screws holding it on.
I am correct. many of the shimano integrated flat bar brake lever+shifters dont have the little access holes.
Heres a picture from my GFs MTB which requires the little indicator on the top to be removed before you can remove the cable. AL1943 is also correct in the fact that they need to be shifted into the smallest cog before the cable can be removed.