To start with, GM advises against any kind of flush, whether by an external machine or by disconnecting the cooler hoses.
So, based on that info, you can drain the fluid, which will get about half of it, drive a few hundred or a thousand miles, then drain it again. This time you'll get a mixture that removes about 25% of the old fluid. If you do it again, you'll get about 12½% old fluid.
Since you have the LS, we can probably assume that you have the 2.4L 4-cylinder engine. You'll find a bolt under the trans that looks similar to this one on my V6 version. You can drain it using that.
So, based on that info, you can drain the fluid, which will get about half of it, drive a few hundred or a thousand miles, then drain it again. This time you'll get a mixture that removes about 25% of the old fluid. If you do it again, you'll get about 12½% old fluid.
Since you have the LS, we can probably assume that you have the 2.4L 4-cylinder engine. You'll find a bolt under the trans that looks similar to this one on my V6 version. You can drain it using that.