Replacing some of the elements of the list

Hello, guys!

please tell me with one question?
initial data
there is a list of the lengths of the lines, divided into groups of 2,3,4,5,6 lengths
only need to select the group where the 4 parameters, and in this group of 4 lengths to find the smallest and replace it with any other. After replacing the list must remain the same?

basically choose from a list where the minimum length of 4 and replace it with a new length?