I was just doing this the other day.
You need an actual converter with power supply, unless your application can output 485 through some of the 232 wires (my company used a HMI that could output 485 through it's 232 port, using only some of the pins).
However, part of the reason 485 is so successful is that it has two wires twisted around each other, which balances the noise on each and allows it to be easily accounted for and cleaned out. 232 wire is not like this; you will accumulate noise far easier with 232 than with 485.
If you have more questions, I can give a more in-depth answer, but it appears that you merely want to obtain a converter (~107 USD) and plug it in, along with a power supply.
PS: Make sure you are using terminating resistors on both ENDS of the 485 cable; 120 Ohms works best; don't worry about the power used, 485 is made to have a resistor at both ends to clean up reflected signals.