How do I can reduce image size from sprite canvas or set maximum size for choosed image?

Hi all, i have app in which player can upload image and i have one issue. Player can upload image with any size, and 128x128px, and 4096x4096px(FileChooser). I will check all variants, like set limit for image size to upload (i don't know how to do it), or change sprite canvas size (i need change canvas sprite size, not just sprite size).