Hello and welcome to JustAnswer!
The upper line is a regular fitting that you would use a wrench for. I'm assuming you are talking about the lower line? This uses a quick connect fitting. Inside the fitting on the hose side there are spring loaded fingers that grab a ridge on the hard fitting coming out of the radiator. You'll need a quick connect removal tool to remove the line.
You can get a set of the tools pretty inexpensively at Sears or a parts store.
You will put the tool over the short hard line coming out of the bottom of the radiator. Push the trans line towards the radiator, the slide the tool up into the quick connect fitting to release the spring tabs. Then you can pull the line off the radiator.