You don't do that (or else you will earn the wrath of Stephen). Not sure why many beginners want to do that. I guess they just aren't thinking ahead.
You return one variable that is a cell array that has a variable number of cells, not a variable number of uniquely-named variables:
function cellArrayA = Level(A,m)
and use parentheses rather than square brackets.
On the other hand, there are functions that return variable numbers of outputs but (I think) that they generally return them all, not a variable number of them. Then it's up to the calling routine to accept the ones you want. For example, the max() function:
maxValue = max(data);
[maxValue, indexOfMax] = max(data) ;