Armor Texturizing

Whenever I try to use an uploaded model to replace a piece of armour, the textures either just bug out and become a big bold of random colors, or the textures dont change at all, and stay the default armour texture… Anybody know how to fix/correctly texture the armour?

somethimes, if you click on the “upload from computer” buttom, you have to restart the page to use it again (because it wont upload the selected image)