How do i edit an order state using the API ?

[J0vis]

Hello,
My boss needs me to create an application to control the stock of products and delivery of orders. I made a lot of progress with the API and right now im able to retrive all the data i need and show on the front-end whatever my boss asks for, but right now i need to actly change the values inside the store on a group of orders, a good example would be: Change all order_states = 21 to order_states = 3. I could not understand how to do the in the documentation, so if anyone can point me in the right direction it would amazing. The application is web based so html, css, php, js. Thanks in advance.
I just finished college and i feel like this is way byond me right now, im the whole "IT sector" here and sincerily i think boss is crazy asking an intern on his first job to manage this much data but... Holy fuck anxiety is way too loud right now sorry.