I had the same question a few months ago if you scroll down.
Go to this website:
How to Replace Nissan Versa Cabin Air Filter | eHow.com
The versa is the same as the cube.
I ordered my filter on ebay. Can't remember which company, but don't buy retail. Way too much $$$$.
In the box of the filter was also directions.
Just watch when you pull the little plastic tab, it will break, ask me.
But, duct tape is a good thing.