Answer:
Net change means the differnce between the before result and the after result. You would subtract the numbers, but if you have a gain(the before result smaller than after result) you would do its absolute value. If it's a loss(the before result bigger than after result) you would put a negative behind its absolute value.
e.g. if 2019 had $1 net worth and 2020 had $2 net worth, since 2>1 it would be |2-1| = 1. If 2019 had $2 net worth and 2020 had $1 net worth, since 1<2 there would be a - |2-1| = -1 net change.
However, if there is no change it would be just 0.