Hello, and thanks for your question! My name is XXXXX XXXXX I am happy to assist you today!!
There are 2 most common ways to cut this type of material.
One way is to use a small 4-4.5 inch hand grinder with a composite abrasive blade for cutting metal
The other most common way is to use your circular saw with the same kind of blade but this one will be 7 inches so that it fits your saw.
You should wear eye and ear protection because its going to a very loud job and sparks will fly around also. So, do not do this in a dry area unless you have a water hose at the ready to wet down the area after you make your cuts. You don't want to start a fire by accident.
These composite blades are pretty cheap and should cost around $2 for the hand grinder blade and about $5 for the circular saw blade.
After you make your cut there are going to be sharp edges that you should file down so you don't get cut by accident.
You could also use the metal cutting hand shears that are common to the market but the results are generally poor when used for longer cuts as your doing, its also harder to cut the unlevel sheets
Your very welcome