unhook one of the lines at the radiator and run the engine for about 4 seconds. Make sure you have a jar or something with a rag to catch the fluid or you will have a mess. I think the bottom line will pump out and the top line is return, so keep that in mind when placing the jar.
make sure you don't run it more than 3 or 4 seconds, you don't want to mess up the pump. If you need to drain more, run the engine normally first for a bit so not to run your trans pump dry.