You can use the delete action if you want to it to look like this after removing the x index starting with 3. All the y and z indexes with the same x will be removed too.
1,6
2,7
4,9
5,10
Adding values to the array is simple as making the array size one bigger and setting the values at the bottom of the array.
However if you want just the values directly below three to be shifted up like so:
1,6
2,7
4,8
5,9
0,10
Then you need to define and empty value like 0, and you need to shift it up manually.
var x=4
var y=3
var z=0
repeat array.width-x times
--- set array at (x+loopindex, y, z) to array.at(x+loopindex+1, y, z)