How can you change a 4 it parallel adder into a 16 bit adder?

To convert a 4-bit parallel adder into a 16-bit adder, you can cascade four 4-bit adders. Connect the carry output of the least significant 4-bit adder to the carry input of the next 4-bit adder, and repeat this for all four adders. This way, each adder handles a portion of the 16-bit input, while the carries are propagated through the chain, allowing for the addition of all 16 bits. Additionally, ensure that the inputs are properly segmented into four groups of four bits each.