You cannot convert a 16 GB pendrive to 32 GB pendrive. Most of the pendrives comes as a single device and won`t give the option to expand the memory. You need to buy another pen drive to fulfill your requirements. If you are having a card reader and a memory card which will also act similar to a pendrive, then you can upgrade using the higher capacity memory card. Memory cards and USB drives are of similar price range considering the similar read/write speed.
1 5 1
It's impossible. You need to buy a new pendrive.