Is it possible to increment or decrement a variable with an event ?

I have a lot of art that I've added to my music library and some of this consists of booklets about albums/artists etc.

I've added it so that it's accessible to a skin via ListItem.Art(bookletN) where N is a number between 1 and whatever.  I've also managed to get a simple window together to show this in.



Where I'm stuck now though is how to get it to show the 'next page' which would be ListItem.Art(booklet2) etc etc. I would like to be able to navigate backwards and forwards through the booklet by clicking on the arrows but I have absolutely no idea if it's even possible to do that, and if so how to go about it.

Any help would be much appreciated. As you can probably tell from the screenshot, my skinning skills are not really up to much!