How to update the kernel for M2Z

(I am new to banana pi, so please excuse me if there are any trivial things) I have a banana pi with a kernel “4.4.55-BPI-M2Z-Kernel”. The OS is Ubuntu 20.04. I need to get the kernel updated to 4.20, I tried the following things without success. Can someone please tell me what is the best way to do it?