How to change template design of AC login page?

Hi, I’ve been contacted by a company that recently installed a Huawei AC6005 access controller for their network. I’ve been reading the documentation and the technician tells me the upgrade allows for file uploading (ZIP format) to the AC, and that should be the way to modify the login template; they want the login to resemble the company’s image, not the blue screen of the AC by default. But so far I cant find documentation about that, but I assume the coding should be html, strict, and follow certain guidelines and cues… Any advice to this? thanks