Hi lee510, thank you for purcashing our assets pack!
If you want the grid size to be 24 x 24 pixel, when created new map make sure you change the tile size both widht and height to 24. Hope that helps :)
I'm sorry I can't open that link because in my country imgur is blocked. If you aploaded somewhere else then we can look into it.
If you have anymore question please let us know!