Can not put Arduino UNO R2's atmega 16U2 into DFU mode

Development Tools IDE 1.x
6

Two ways. One it if you have a spare Arduino and (6) female/male jumpers we can turn that spare into an ISP.

Second is get a dedicated USBtinyISP or AVRISP Mk II:

Your regional Arduino/electronics distributor should have one or the other.