Because the second tensor has less values contained, u cannot change the shape without losing some of the values in the first tensor. Let’s say the shape of A is (1, 3, 320, 320), the desired shape is (1, 2, 320, 320), a simple way to do so is  by slicing:
START, END = 0, 2
#[START, END)
b = A[ : , START:END, : , : ]