How do you change array size?

Yes you can write to any dimension without being limited by array starting size.
Writing to an index outside the array current dimension will "expand" the array to the biggest index
While there's no way to "reduce" the array indices, other than destroying and recreating the array.

The only concern you have with array dimension is that "expanding" the array is a (relatively) heavy operation,
so it's good practice to not "expand" very frequently.
If you know you're going to write lots of data sequentially,
better start with a relatively big dimensioned array,
or (if you can) write first to the "biggest" index,
so you will expand the array only once
(writing from smallest to biggest would sequentially expand one time x operation, making it much more heavy to process)

Well, this is not a "big" concern if your game is not very resource demanding,
in this case you can safely forget about this matter X)