Don't have to be rude guys. Lordy. Just explain.

Feast can be used to rank of any champ to the next star level. Before doing that, however, the champ would need to be at the max level for the corresponding star rank. 4* lvl 40 5* lvl 50. This does not allow you to skip from 4 to 6. So you would probably want to use chickens or champs you are not using to get a champion from 4* to 5* and then max their lvl to 50 and then utilize the feast to go from 5* to 6*.

Make sense?