As far as cleaning the cage of a Green Cheek, or ANY species of Parrot, you need to clean the cage at least once a week, and by "clean" I mean actually scrub the entire cage and everything in it...As far as changing the NEWSPAPER, BUTCHER PAPER, OR PAPER CAGE-LINERS IN THE BOTTOM OF THE CAGE UNDER THE GRATE, your best bet is to change them every single day, that way your job of doing an entire cage-cleaning will be much, much easier, there will be no smell, and your bird isn't going to be constantly inhaling the dust from dried droppings, which can cause Upper Respiratory Infections, Sinus Infections, Allergy reactions, etc. in both your Birds and you!
***YOU DO NOT EVER WANT TO USE/PUT ANY TYPE OF "SUBSTRATE", AS YOU USED THE TERM, IN THE BOTTOM OF YOUR BIRD'S CAGE!!!! THAT'S A HUGE NO-NO FOR A NUMBER OF IMPORTANT AND SOMETIMES LIFE-THREATENING REASONS!!! You should not EVER use any type of "Substrate" in the bottom of a bird's/parrot's cage (FIRST OF ALL IT'S NASTY!!! IT IS NOT EASIER BUT RATHER WAY MORE WORK THAN SIMPLY USING SHEETS OF EITHER NEWSPAPER, BUTCHER PAPER, PAPER CAGE-LINERS, ETC.)...With using only sheets of Newspaper, Butcher Paper, any other type of sheet-paper, paper Cage Liners, etc., all you have to do is literally just slide the clean sheets of paper in the bottom Tray of the cage, which should be UNDER THE GRATE so that your bird cannot get ahold of the paper and shred them to make a nest or eat, and then each day all you do is slide out the dirty sheets of paper, throw them away, and slide clean sheets of paper in! That's it!!! If you do this every morning after your bird does his first morning poop (the BIG one of the day), then it's no deal at all..If you wait it iis a huge deal...But with any type off "Substrate" it's not only inappropriate for your bird and can/almost ALWAYS WILL cause severe hormonal-behavior, aggression, and Egg-production in females as well as cause Bowel-Obstructions, Crop-Impactions, Poisoning/Toxicity, Choking, etc., but there is not one single type of "Substrate" that doesn't get horribly nasty and become a huge mess at the end of one single day in a bird cage!!! Between their droppings, their food, and their water (which they take baths in and are constantly knocking all over the place), any type of Substrates become a nasty, smelly, dangerous, and often lethal/fatal mess...
***DO NOT EVER PUT ANY OF THE FOLLOWING IN THE BOTTOM OF YOUR BIRD'S/PARROT'S CAGE: No Rodent Bedding of any kind OR Wood Chips of any kind (both often cause bird's upper-respiratory issues and have toxic scents due to oils in the wood), No Crushed Walnut Shell Bedding OR Corn-Cob Bedding (**Both of these are the ones that often kill pet birds/parrots, along with pet Reptiles and Amphiibians), No Shredded-Paper Bedding such as Carefresh (Seen as/Used as Nesting-Material and is a HUGE Trigger of constant Hormonal-Behavior), No Sand, Dirt, Stones, Gravel, or any other loose Substrates of any kind at all OTHER THAN SHEETS OF PAPER/NEWSPAPER/PAPER CAGE LINERS!!!