What happens if the rules call for me to step up a d12, or step down a d4?

If you are called upon to step up a d12, you may add an additional die as appropriate. Stepping up one die type (⇧1) would add a d4 to your pool. ⇧2 would add a d6, and so on.

If you are told to step down a d4, simply remove the die from the die pool altogether.

The one exception to this is during character creation, when choosing your weak area for tradecraft. If your character already has a d4 in a tradecraft area, it may not be chosen as their weak area.