Hey Andy D,
Unfortunately, you cannot... but you do have some workarounds!
Try clicking on your tiles, the little dropdown arrow and then "floating". This will allow you to resize to the size you want.
You also can add objects (bottom left) in order to reshape your dashboard.
Let me know if these helped you!
Ok thank you for the tips!
Sorry to revive a year+ old thread but thought I'd post this as it comes up on my searches.
I have a quick and admittedly dirty solution to this problem and have posted a document about this on:
Hope this helps anyone else that finds this thread