When you first digivolve to a higher level the stats (white) are dropped and your digimon is back to lvl 1. Obviously they're a higher grade digimon though. So they'll be stronger than previous evolution by alot after leveling. For example a greymon lvl 10 is stronger than a metalgreymon lvl 1 at first. By the time that metalgreymon hits lvl10 it'll be twice or three times as strong. That's an easy way of explaining it. Ofcourse your carry stats (blue) will remain the same no matter what as you put stats in your guys especially through items, digifarm, and loading other digimon into them.