VERTICAL SPACING
Select your collection view in the storyboard.
Then change...
Changing
To
I also found this answer, might also be useful
HORIZONTAL SPACING
For Left to Right Spacing, from my testing you can only change the distance from the screen edge to first cell, called Section Insets. You can also change the min spacing between the cells, from 0 to x using Min Spacing For Cells
Setting the collection view to these settings produces
Changing the Min Cell Spacing to:
From this, it appears that you can only adjust the insets on the left and right (padding) from the first and last cell and then the minimum distance between cell. The rest is automatically calculated.
So to get the desired effect you need to alter these values, Min Spacing For Cells and the Section Insets