No, it is not possible to upgrade the processor in any of the NUCs. They are permanently mounted on the board. Your only real choice is to purchase a replacement unit. There are lots of NUC models with 5th and 6th generation Intel Core i3, i5 and i7 processors to choose from. The 6th generation models require DDR4 memory, which means you cannot use the (DDR3L) memory that you have in the PY NUC.
Hope this helps,